Display device

ABSTRACT

A display device that can easily achieve higher definition is provided The display device includes a pixel, a first wiring, and a second wiring. The pixel includes first to fourth transistors, a first capacitor, and a light-emitting element. One of a source and a drain of the first transistor is connected to the first wiring, and the other of the source and the drain of the first transistor is connected to a gate of the second transistor and to the first capacitor. The light-emitting element is connected to one of a source and a drain of the second transistor. The first wiring is supplied with a first data potential. The second wiring is supplied with a second data potential and a reset potential in different periods. The third transistor supplies the second data potential to the first capacitor. The fourth transistor supplies the reset potential to the light-emitting element.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.17/003,655, filed Aug. 26, 2020, now allowed, which claims the benefitof foreign priority applications filed in Japan as Serial No.2020-082434 on May 8, 2020, and Serial No. 2019-157094 on Aug. 29, 2019,all of which are incorporated by reference.

BACKGROUND OF THE INVENTION 1. Field of the Invention

One embodiment of the present invention relates to a display device. Oneembodiment of the present invention relates to a display device with animaging function.

Note that one embodiment of the present invention is not limited to theabove technical field. Examples of the technical field of one embodimentof the present invention disclosed in this specification and the likeinclude a semiconductor device, a display device, a light-emittingdevice, a power storage device, a memory device, an electronic device, alighting device, an input device, an input/output device, a drivingmethod thereof, and a manufacturing method thereof. A semiconductordevice refers to a device that can function by utilizing semiconductorcharacteristics in general.

2. Description of the Related Art

In recent years, display devices have been required to have higherdefinition in order to display high-resolution images. In addition,display devices used in information terminals such as smartphones,tablet terminals, and laptop personal computers (PCs) have been requiredto have higher definition and lower power consumption. Furthermore,display devices have been required to have a variety of functions suchas a touch panel function and a function of capturing images offingerprints for authentication in addition to a function of displayingimages.

Light-emitting devices including light-emitting elements have beendeveloped as display devices. Light-emitting elements utilizingelectroluminescence (hereinafter referred to as EL elements) havefeatures such as ease of reduction in thickness and weight, high-speedresponse to input signals, and capability of DC low voltage driving, andhave been used in display devices. Patent Document 1, for example,discloses a flexible light-emitting device in which an organic ELelement is used.

REFERENCE Patent Document

Patent Document 1: Japanese Published Patent Application No. 2014-197522

SUMMARY OF THE INVENTION

One object of one embodiment of the present invention is to provide adisplay device that can easily achieve higher definition. Another objectof one embodiment of the present invention is to provide a displaydevice whose power consumption can be reduced.

Another object of one embodiment of the present invention is to providea display device that can function as a touch panel. Another object ofone embodiment of the present invention is to provide a display devicewith an imaging function.

Note that the description of these objects does not disturb theexistence of other objects. One embodiment of the present invention doesnot need to achieve all the objects. Objects other than these can bederived from the description of the specification, the drawings, theclaims, and the like.

One embodiment of the present invention is a display device including apixel, a first wiring, and a second wiring. The pixel includes first tofourth transistors, a first capacitor, and a light-emitting element. Oneof a source and a drain of the first transistor is electricallyconnected to the first wiring, and the other of the source and the drainof the first transistor is electrically connected to a gate of thesecond transistor and one electrode of the first capacitor. Oneelectrode of the light-emitting element is electrically connected to oneof a source and a drain of the second transistor. The first wiring has afunction of being supplied with a first data potential. The secondwiring has a function of being supplied with a second data potential anda reset potential in different periods. The third transistor has afunction of supplying the second data potential supplied to the secondwiring to the other electrode of the first capacitor when the thirdtransistor is in an on state. The fourth transistor has a function ofsupplying the reset potential supplied to the second wiring to the oneelectrode of the light-emitting element when the fourth transistor is inan on state.

Another embodiment of the present invention is a display deviceincluding a pixel, a first wiring, and a second wiring. The pixelincludes first to fourth transistors, a first capacitor, and alight-emitting element. One of a source and a drain of the firsttransistor is electrically connected to the first wiring, and the otherof the source and the drain of the first transistor is electricallyconnected to a gate of the second transistor and one electrode of thefirst capacitor. One electrode of the light-emitting element iselectrically connected to one of a source and a drain of the secondtransistor. The first wiring has a function of being supplied with afirst data potential. The second wiring has a function of being suppliedwith a second data potential and a reset potential in different periods.One of a source and a drain of the third transistor is electricallyconnected to the second wiring, and the other of the source and thedrain of the third transistor is electrically connected to the otherelectrode of the first capacitor. One of a source and a drain of thefourth transistor is electrically connected to the second wiring, andthe other of the source and the drain of the fourth transistor iselectrically connected to the one electrode of the light-emittingelement.

Another embodiment of the present invention is a display deviceincluding a pixel, a first wiring, and a second wiring. The pixelincludes first to fourth transistors, a first capacitor, and alight-emitting element. One of a source and a drain of the firsttransistor is electrically connected to the first wiring, and the otherof the source and the drain of the first transistor is electricallyconnected to a gate of the second transistor and one electrode of thefirst capacitor. One electrode of the light-emitting element iselectrically connected to one of a source and a drain of the secondtransistor. The first wiring has a function of being supplied with afirst data potential. The second wiring has a function of being suppliedwith a second data potential and a reset potential in different periods.One of a source and a drain of the third transistor is electricallyconnected to the second wiring, and the other of the source and thedrain of the third transistor is electrically connected to the otherelectrode of the first capacitor and one of a source and a drain of thefourth transistor. The other of the source and the drain of the fourthtransistor is electrically connected to the one electrode of thelight-emitting element.

In the above, a third wiring and a fourth wiring are preferablyincluded. The third wiring is electrically connected to a gate of thefirst transistor and a gate of the fourth transistor. The fourth wiringis electrically connected to a gate of the third transistor.

In the above, a second capacitor is preferably further included. Oneelectrode of the second capacitor is electrically connected to the gateof the second transistor, and the other electrode of the secondcapacitor is electrically connected to the one electrode of thelight-emitting element.

In the above, a plurality of pixels are preferably included. In thatcase, the plurality of pixels are arranged in a matrix in a rowdirection and a column direction. The second wiring is preferablyelectrically connected to the third transistor and the fourth transistorin each of two or more pixels among the plurality of pixels arranged inthe row direction.

Alternatively, the second wiring is preferably electrically connected tothe third transistor and the fourth transistor in each of three adjacentpixels among the plurality of pixels arranged in the row direction. Inthat case, the three adjacent pixels preferably emit light of differentcolors.

In the above, a light-receiving element is preferably further included.In that case, the light-receiving element has a function of receivinglight emitted from the light-emitting element. In addition, thelight-emitting element and the light-receiving element are preferablyprovided on the same plane.

In the above, in the light-emitting element, a first electrode, alight-emitting layer, and a common electrode are preferably stacked. Inthe light-receiving element, a second electrode, an active layer, andthe common electrode are preferably stacked. In that case, it ispreferable that the light-emitting layer and the active layer containdifferent organic compounds, the first electrode and the secondelectrode be provided on the same plane to be apart from each other, andthe common electrode be provided to cover the light-emitting layer andthe active layer.

In the above, in the light-emitting element, a first electrode, a commonlayer, a light-emitting layer, and a common electrode are preferablystacked. In the light-receiving element, a second electrode, the commonlayer, an active layer, and the common layer are preferably stacked. Inthat case, it is preferable that the light-emitting layer and the activelayer contain different organic compounds, the first electrode and thesecond electrode be provided on the same plane to be apart from eachother, the common electrode be provided to cover the light-emittinglayer and the active layer, and the common layer be provided to coverthe first electrode and the second electrode.

One embodiment of the present invention can provide a display devicethat can easily achieve higher definition. Alternatively, one embodimentof the present invention can provide a display device whose powerconsumption can be reduced.

Alternatively, one embodiment of the present invention can provide adisplay device that can function as a touch panel. Alternatively, oneembodiment of the present invention can provide a display device with animaging function.

Note that the description of the effects does not disturb the existenceof other effects. One embodiment of the present invention does not needto have all the effects. Effects other than these can be derived fromthe description of the specification, the drawings, the claims, and thelike.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1A is a block diagram of a display device, and FIG. 1B is a pixelcircuit diagram;

FIG. 2 is a timing chart illustrating a method for driving the displaydevice;

FIG. 3 is a pixel circuit diagram;

FIGS. 4A and 4B are pixel circuit diagrams;

FIG. 5 is a block diagram of a display device;

FIG. 6 is a pixel circuit diagram;

FIG. 7 is a pixel circuit diagram;

FIGS. 8A and 8B are timing charts each illustrating a method for drivingthe display device;

FIGS. 9A and 9B are block diagrams of display devices;

FIGS. 10A and 10B are block diagrams of display devices;

FIG. 11A is a pixel circuit diagram, and FIG. 11B is a timing chartillustrating a method for driving the display device;

FIG. 12 is a pixel circuit diagram;

FIG. 13 is a timing chart illustrating a method for driving the displaydevice;

FIGS. 14A, 14B, 14D, and 14F to 14H each show a structure example of adisplay device, and FIGS. 14C and 14E each show an example of an image;

FIGS. 15A to 15D each show a structure example of a display device;

FIGS. 16A to 16C each show a structure example of a display device;

FIGS. 17A and 17B each show a structure example of a display device;

FIGS. 18A to 18C each show a structure example of a display device;

FIG. 19 shows a structure example of a display device;

FIG. 20 shows a structure example of a display device;

FIGS. 21A and 21B each show a structure example of a display device;

FIGS. 22A and 22B each show a structure example of a display device;

FIG. 23 shows a structure example of a display device;

FIGS. 24A and 24B each show a structure example of an electronic device;

FIGS. 25A to 25D show structure examples of electronic devices;

FIGS. 26A to 26F show structure examples of electronic devices; and

FIGS. 27A to 27C show results of imaging in Example.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments will be described below with reference to the drawings. Notethat the embodiments can be implemented with many different modes, andit will be readily understood by those skilled in the art that modes anddetails thereof can be changed in various ways without departing fromthe spirit and scope thereof. Therefore, the present invention shouldnot be construed as being limited to the description of embodimentsbelow.

Note that in structures of the invention described below, the sameportions or portions having similar functions are denoted by the samereference numerals in different drawings, and the description thereof isnot repeated. Moreover, similar functions are denoted by the same hatchpattern and are not denoted by specific reference numerals in somecases.

Note that in each drawing described in this specification, the size, thelayer thickness, or the region of each component is exaggerated forclarity in some cases. Therefore, the size, the layer thickness, or theregion is not limited to the illustrated scale.

Note that in this specification and the like, ordinal numbers such as“first” and “second” are used in order to avoid confusion amongcomponents and do not limit the number of components.

A transistor is a kind of semiconductor elements and can achieveamplification of current or voltage, switching operation for controllingconduction or non-conduction, or the like. A transistor in thisspecification includes, in its category, an insulated-gate field effecttransistor (IGFET) and a thin film transistor (TFT).

Furthermore, functions of a source and a drain might be interchangedwith each other when a transistor of opposite polarity is employed orwhen the direction of current is changed in circuit operation, forexample. Therefore, the terms “source” and “drain” can be interchangedwith each other in this specification.

Note that in this specification, an EL layer means a layer containing atleast a light-emitting substance (also referred to as a light-emittinglayer) or a stack including the light-emitting layer provided between apair of electrodes of a light-emitting element.

In this specification and the like, a display panel that is oneembodiment of a display device has a function of displaying (outputting)an image or the like on (to) a display surface. Thus, the display panelis one embodiment of an output device.

Furthermore, in this specification and the like, a substrate of adisplay panel to which a connector such as an FPC (Flexible PrintedCircuit) or a TCP (Tape Carrier Package) is attached, or a substrate onwhich an IC is mounted by a COG (Chip On Glass) method or the like isreferred to as a display panel module, a display module, or simply adisplay panel or the like in some cases.

Note that in this specification and the like, a touch panel that is oneembodiment of a display device has a function of displaying an image orthe like on a display surface and a function of a touch sensor capableof sensing the contact, press, approach, or the like of a sensing targetsuch as a finger or a stylus with or to the display surface. Therefore,the touch panel is one embodiment of an input/output device.

A touch panel can also be referred to as, for example, a display panel(or a display device) with a touch sensor or a display panel (or adisplay device) having a touch sensor function. A touch panel caninclude a display panel and a touch sensor panel. Alternatively, a touchpanel can have a function of a touch sensor inside a display panel or ona surface thereof.

Furthermore, in this specification and the like, a substrate of a touchpanel to which a connector or an IC is attached is referred to as atouch panel module, a display module, or simply a touch panel or thelike in some cases.

Embodiment 1

In this embodiment, structure examples and driving method examples of adisplay device according to one embodiment of the present invention willbe described.

One embodiment of the present invention is a display device thatincludes a plurality of pixels arranged in a matrix. The pixel includesfirst to fourth transistors, a capacitor, and a light-emitting element.The display device further includes a first wiring and a second wiringthat are electrically connected to the pixels.

The second transistor has a function of controlling current flowingthrough the light-emitting element and functions as a drivingtransistor. The first transistor functions as a switch for controllingthe conduction and non-conduction between the first wiring and a gate ofthe second transistor. The first wiring is supplied with a first datapotential, and the first data potential can be applied to the gate ofthe second transistor through the first transistor when the firsttransistor is turned on (is brought into conduction).

The second wiring is supplied with a second data potential and a resetpotential in different periods.

One electrode (also referred to as a first electrode) of the capacitoris electrically connected to the gate of the second transistor. Thethird transistor functions as a switch for controlling the conductionand non-conduction between the other electrode (also referred to as asecond electrode) of the capacitor and the second wiring. The seconddata potential can be applied to the second electrode of the capacitorthrough the third transistor when the third transistor is turned on.

After the first data potential is applied to the gate of the secondtransistor, the first transistor is turned off (is brought out ofconduction) to bring the gate of the second transistor into a floatingstate, and the second data potential is applied to the second electrodeof the capacitor through the third transistor. Accordingly, a potentialof the gate of the second transistor can be changed from the first datapotential depending on the second data potential by capacitive couplingthrough the capacitor.

In this manner, the pixel can generate a potential to be supplied to agate of the driving transistor (the second transistor) of thelight-emitting element by a combination of two kinds of data potentials.For example, gradation correction can be performed with the second datapotential. In addition, the pixel in the display device can generate apotential higher than the maximum potential that can be supplied from adriver circuit (a source driver circuit) for supplying the first datapotential and the second data potential. Accordingly, the power supplyvoltage of the driver circuit can be lowered, and the power consumptionof the driver circuit can be reduced.

The fourth transistor functions as a switch for supplying the resetpotential to be supplied to the second wiring to the one electrode (thefirst electrode) of the light-emitting element. When the reset potentialis applied to the second wiring, the fourth transistor is turned on, sothat the reset potential is applied to the first electrode of thelight-emitting element. When the first data potential and the resetpotential are supplied in the same period, the gate-source voltage ofthe second transistor can be determined regardless of electricalcharacteristics of the light-emitting element. Thus, high-qualitydisplay can be achieved.

In the display device according to one embodiment of the presentinvention, the second wiring can function as a wiring for supplying thesecond data potential and a wiring for supplying the reset potential.Accordingly, even in a multifunctional display device, the number ofwirings can be reduced, so that higher definition can be achieved.

In addition, the second wiring may be a wiring for supplying the seconddata potential and the reset potential to two or more pixels. This ispreferable because the number of wirings included in the display devicecan be further reduced.

Here, the third transistor may be provided between the second wiring andthe fourth transistor, and the reset potential may be supplied from thesecond wiring to the first electrode of the light-emitting element wheneach of the third transistor and the fourth transistor is in an onstate. Accordingly, the number of wirings provided in the pixel can bereduced, so that higher definition can be achieved more easily.

Alternatively, a structure may be employed in which the second wiringand one of a source and a drain of the fourth transistor areelectrically connected to each other and the third transistor is notprovided between the second wiring and the one of the source and thedrain of the fourth transistor. Accordingly, a difference between thereset potential applied to the second wiring and a potential applied tothe first electrode of the light-emitting element can be made smallerthan that in the case where the reset potential is supplied through twotransistors.

More specific examples are described below with reference to drawings.

STRUCTURE EXAMPLE 1

FIG. 1A is a block diagram of a display device 10. The display device 10includes a display portion 11, a driver circuit portion 12, and a drivercircuit portion 13.

In the display portion 11, a plurality of pixels 21 are arranged in amatrix. The pixel 21 is electrically connected to wirings SL, VL, GL1,and GL2. The wirings SL and VL are electrically connected to the drivercircuit portion 12. The wirings GL1 and GL2 are electrically connectedto the driver circuit portion 13. The driver circuit portion 12functions as a source line driver circuit (also referred to as a sourcedriver). The driver circuit portion 13 functions as a gate line drivercircuit (also referred to as a gate driver).

PIXEL CONFIGURATION EXAMPLE 1-1

FIG. 1B shows an example of a circuit diagram of the pixel 21. The pixel21 includes a transistor M1, a transistor M2, a transistor M3, atransistor M4, a capacitor C1, a capacitor C2, and a light-emittingelement EL.

A gate of the transistor M1 is electrically connected to the wiring GL1.One of a source and a drain of the transistor M1 is electricallyconnected to the wiring SL. The other of the source and the drain of thetransistor M1 is electrically connected to one electrode (a firstelectrode) of the capacitor C1, one electrode (a first electrode) of thecapacitor C2, and a gate of the transistor M2. One of a source and adrain of the transistor M2 is electrically connected to a wiring AL. Theother of the source and the drain of the transistor M2 is electricallyconnected to one electrode (an anode electrode or a first electrode) ofthe light-emitting element EL. A gate of the transistor M3 iselectrically connected to the wiring GL2. One of a source and a drain ofthe transistor M3 is electrically connected to the wiring VL. The otherof the source and the drain of the transistor M3 is electricallyconnected to the other electrode (a second electrode) of the capacitorC1. A gate of the transistor M4 is electrically connected to the wiringGL1. One of a source and a drain of the transistor M4 is electricallyconnected to the wiring VL. The other of the source and the drain of thetransistor M4 is electrically connected to the one electrode of thelight-emitting element EL, the other electrode (a second electrode) ofthe capacitor C2, and the one of the source and the drain of thetransistor M3. The other electrode (a cathode electrode or a secondelectrode) of the light-emitting element EL is electrically connected toa wiring CL.

The transistors M1, M3, and M4 function as switches. The transistor M2functions as a transistor for controlling current flowing through thelight-emitting element EL.

A data potential D (also referred to as a first data potential) isapplied to the wiring SL. A data potential D_(W) (also referred to as asecond potential potential) and a reset potential V_(R) are applied tothe wiring VL in different periods. Different selection signals aresupplied to the wirings GL1 and GL2. The selection signals include apotential for turning on a transistor and a potential for turning offthe transistor.

The wiring AL is a wiring to which an anode potential is applied. Thewiring CL is a wiring to which a cathode potential is applied. In thepixel 21, the anode potential is higher than the cathode potential.

Here, as shown in FIG. 1B, a node to which the gate of the transistor M2is connected is referred to as a node N1.

Note that in this specification and the like, a node is an element(e.g., a wiring) that enables electrical connection between elementsincluded in a circuit. Thus, a “node to which A is connected” is awiring that is electrically connected to A and can be regarded as havingthe same potential as A. Note that even when one or more elements thatenable electrical connection (e.g., switches, transistors, capacitors,inductors, resistors, or diodes) are inserted in a portion of thewiring, the wiring can be regarded as the “node to which A is connected”as long as it can be regarded as having the same potential as A.

Here, a transistor with extremely low off-state leakage current ispreferably used as each of the transistors M1, M3, and M4 functioning asswitches. In particular, a transistor including an oxide semiconductorin a semiconductor layer where a channel is formed can be favorablyused. It is preferable to use a transistor including an oxidesemiconductor as the transistor M2 because all the transistors can beformed through the same manufacturing steps. Note that the transistor M2may be formed using silicon (including amorphous silicon,polycrystalline silicon, or single crystal silicon) in a semiconductorlayer where a channel is formed. Alternatively, all the transistors canbe formed using silicon.

Driving Method Example 1

An example of a method for driving the pixel 21 shown in FIG. 1B isdescribed with reference to a timing chart in FIG. 2 . FIG. 2 showssignals input to the wirings GL1, GL2, SL, and VL and an example of achange in the potential of the node N1.

Note that in the following description, the influence of the thresholdvoltage of the transistor, the on-state resistance of the transistor,the gate capacitance of the transistor, wiring resistance, parasiticcapacitance, and the like is not considered for simplification of thedescription.

<Before Time T1>

Before Time T1, a potential for turning off the transistor (here, alow-level potential) is applied to the wirings GL1 and GL2. Data to bewritten to pixels in the previous row is supplied to the wirings SL andVL. As the potential of the node N1, a potential Vx that is written inthe previous frame is applied.

<Period T1-T2>

At Time T1, a potential for turning on the transistor (here, ahigh-level potential) is applied to the wirings GL1 and GL2, the datapotential D is applied to the wiring SL, and the reset potential V_(R)is applied to the wiring VL.

In the period T1-T2, the transistors M1, M3, and M4 are turned on. Thereset potential V_(R) is supplied to the first electrode of thelight-emitting element EL and the second electrode of the capacitor C2through the transistor M4. The reset potential V_(R) is supplied to thesecond electrode of the capacitor C1 through the transistor M3. The datapotential D is supplied to the node N1 through the transistor M1.

As described above, when the data potential D is written to the node N1,the reset potential V_(R) is written to a node to which the anodeelectrode of the light-emitting element EL is connected, so that apotential difference between this node and the node N1, that is,gate-source voltage of the transistor M2 can be determined regardless ofthe electrical state of the light-emitting element EL. Specifically, thegate-source voltage of the transistor M2 is D-V_(R) with the resetpotential V_(R) used as a reference.

In addition, charge is stored in the capacitor C1 depending on apotential difference between the data potential D and the resetpotential V_(R).

Note that at this time, the reset potential V_(R) is applied to theanode electrode of the light-emitting element EL. When the resetpotential V_(R) is set so that voltage between the pair of electrodes ofthe light-emitting element EL does not exceed the threshold voltage ofthe light-emitting element EL, light is not emitted from thelight-emitting element EL.

<Period T2-T3>

Then, at Time T2, a low-level potential is applied to the wiring GL1, ahigh-level potential is applied to the wiring GL2, and the datapotential D_(W) is applied to the wiring VL.

When the wiring GL1 has a low-level potential, the transistors M1 and M4are turned off. Accordingly, the node N1 is brought into a floatingstate.

The data potential D_(W) is applied to the second electrode of thecapacitor C1 through the transistor M3. Since the voltage D-V_(R) isstored in the capacitor C1, the potential of the node N1 changes fromthe data potential D into a potential V_(D+W) by capacitive couplingwhen the potential of the second electrode of the capacitor C1 changesfrom the reset potential V_(R) into the data potential D_(W). Here, theamount of change in the potential of the node N1 (i.e., a differencebetween the potential V_(D+)w and the data potential D) is substantiallydetermined by the capacitance of the capacitor C1 and the capacitance ofthe capacitor C2. In the case where the capacitance of the capacitor C1is much larger than the capacitance of the capacitor C2, the amount ofchange in the potential of the node N1 is closer to a difference betweenthe data potential D_(W) and the reset potential V_(R).

Thus, the potential V_(D+W) is applied to the gate of the transistor M2.When current corresponding to the potential flows to the light-emittingelement EL through the transistor M2, the light-emitting element EL canemit light.

For example, by applying a high-level potential as the data potentialD_(W), the emission luminance of the light-emitting element EL can beincreased. In contrast, by applying a low-level potential as the datapotential D_(W), the emission luminance of the light-emitting element ELcan be decreased.

With such a driving method, emission luminance can be adjusted for eachof the pixels 21, so that what is called pixel dimming can be achieved.Luminance is optimally corrected in accordance with an image to bedisplayed, so that high-quality display can be achieved. In addition, ina conventional display device, video data needs to be generated byaddition of data for display and data for correction and needs to besupplied to pixels. In contrast, in one embodiment of the presentinvention, data for display and data for correction can be independentlysupplied, so that a configuration of a driver circuit or the like can besimplified.

<At and After Time T3>

At Time T3, a low-level potential is applied to the wiring GL2. Thus,operation of writing data to the pixels 21 is completed. After Time T3,writing operation for the next row is performed.

The above is the description of the example of the method for drivingthe pixel 21.

Modification Example 1

FIG. 3 is a circuit diagram of a pixel 21 a that is a modificationexample of the pixel 21 shown in FIG. 1B.

In an example of the pixel 21 a, the transistors M1 to M4 each include aback gate. A pair of gates of each transistor is electrically connectedto each other. Thus, the on-state current of the transistor can beincreased and saturation characteristics can be improved, so that adisplay device that has higher reliability can be achieved.

Note that although the pair of gates of each transistor is electricallyconnected to each other here, one embodiment of the present invention isnot limited thereto. The pixel 21 a may include a transistor in whichone of gates is connected to another wiring. For example, when one of apair of gates of a transistor is connected to a wiring to which a fixedpotential is applied, the stability of electrical characteristics can beimproved. Alternatively, one of a pair of gates of a transistor may beconnected to a wiring to which a potential for controlling the thresholdvoltage of the transistor is applied.

Although the example in which the four transistors each include a backgate is shown here, a transistor that includes a back gate and atransistor that does not include a back gate may be used in combination.

Pixel Configuration Example 1-2

A configuration example of a pixel that is partly different from theconfiguration of the pixel shown in FIG. 1B is described below.

FIG. 4A shows a circuit diagram of the pixel 21 b. The pixel 21 bdiffers from the pixel 21 mainly in connection between the capacitor C1and the transistors M3 and M4.

The gate of the transistor M3 is electrically connected to the wiringGL2. The one of the source and the drain of the transistor M3 iselectrically connected to the wiring VL. The other of the source and thedrain of the transistor M3 is electrically connected to the secondelectrode of the capacitor C1 and the one of the source and the drain ofthe transistor M4. For other connection relationships, the descriptionof the pixel 21 in FIG. 1B can be referred to.

In the pixel 21 b, the second electrode of the capacitor C1, the otherof the source and the drain of the transistor M3, and the one of thesource and the drain of the transistor M4 are electrically connected toeach other. This structure can simplify wirings in the pixel 21 b andthus is suitable for higher definition.

The pixel 21 b includes two transistors (the transistors M3 and M4)between the wiring VL and the anode electrode of the light-emittingelement EL.

Modification Example 2

FIG. 4B is a circuit diagram of a pixel 21 c that is a modificationexample of the pixel 21 b shown in FIG. 4A.

In an example of the pixel 21 c, the transistors M1 to M4 each include aback gate. As in the pixel 21 a (see FIG. 3 ), a pair of gates of eachtransistor is electrically connected to each other.

Note that as in the pixel 21 a, not all the transistors necessarily havea structure where the pair of gates is electrically connected to eachother, and a transistor that is connected to another wiring may beincluded. In addition, not all the transistors necessarily include backgates, and a transistor that includes a back gate and a transistor thatdoes not include a back gate may be used in combination.

Driving method example 1 can be referred to for examples of methods fordriving the pixels 21 b and 21 c.

The above is the description of Structure example 1.

Structure Example 2

A structure example of a display device that is partly different fromStructure example 1 is described below. Note that portions similar tothose described above are not described below in some cases.

FIG. 5 is a block diagram of a display device 10 a. The display device10 a includes a display portion 11 a, the driver circuit portion 12, andthe driver circuit portion 13. The display portion 11 a includes aplurality of pixels 20 arranged in a matrix.

The pixels 20 each include a subpixel 21R, a subpixel 21G, and asubpixel 21B. For example, the subpixel 21R exhibits a red color, thesubpixel 21G exhibits a green color, and the subpixel 21B exhibits ablue color. Thus, the display device 10 a can perform full-colordisplay. Note that although the example where the pixels 20 each includesubpixels of three colors is shown here, subpixels of four or morecolors may be included.

The wirings GL1 and GL2 are electrically connected to the subpixels 21R,21G, and 21B arranged in a row direction (an extending direction of thewiring GL1 or the like). Wirings SLR, SLG, and SLB are electricallyconnected to the subpixels 21R, 21G, and 21B arranged in a columndirection (an extending direction of the wiring VL or the like),respectively. The wiring VL is electrically connected to the pixels 20arranged in the column direction. The wiring VL is also electricallyconnected to the subpixels 21R, 21G, and 21B included in the pixel 20.

Pixel Configuration Example 2-1

FIG. 6 shows an example of a circuit diagram of the pixel 20. The pixels20 each include the subpixels 21R, 21G, and 21B.

The pixel 20 shown in FIG. 6 is an example in which the configuration ofthe pixel 21 a shown in FIG. 3 is used for each of the subpixels 21R,21G, and 21B. Note that each of the transistors included in thesubpixels does not necessarily include a back gate. Alternatively, theconfiguration of the pixel 21 shown in FIG. 1B may be used for each ofthe subpixels 21R, 21G, and 21B.

The subpixel 21R includes a light-emitting element ELR emitting redlight. The subpixel 21G includes a light-emitting element ELG emittinggreen light. The subpixel 21B includes a light-emitting element ELBemitting blue light. Note that the pixel 20 may include a subpixelincluding a light-emitting element emitting light of another color. Forexample, the pixel 20 may include, in addition to the three subpixels, asubpixel including a light-emitting element emitting white light or asubpixel including a light-emitting element emitting yellow light.

The wiring VL is electrically connected to the one of the source and thedrain of each of the transistors M3 included in the subpixels 21R, 21G,and 21B. With such a structure, the number of wirings VL can be reducedto one-third of the number of wirings VL in the structure described inStructure example 1, so that a display device with higher definition canbe achieved.

Pixel Configuration Example 2-2

FIG. 7 shows an example of a circuit diagram of a pixel 20 a. The pixel20 a includes a subpixel 21 aR, a subpixel 21 aG, and a subpixel 21 aB.

The pixel 20 a shown in FIG. 7 is an example in which the configurationof the pixel 21 c shown in FIG. 4B is used for each of the subpixels 21aR, 21 aG, and 21 aB. Note that each of the transistors included in thesubpixels does not necessarily include a back gate. Alternatively, theconfiguration of the pixel 21 b shown in FIG. 4A may be used for each ofthe subpixels 21 aR, 21 aG, and 21 aB.

Like the pixel 20, the pixel 20 a shown in FIG. 7 can have a reducednumber of wirings VL and thus can be regarded as being suitable forhigher definition.

Driving Method Example 2-1

An example of a method for driving the pixel 20 shown in FIG. 6 isdescribed below with reference to a timing chart in FIG. 8A. FIG. 8Ashows signals input to the wirings GL1, GL2, SLR, SLG, SLB, and VL.

<Before Time T11>

Before Time T11, a potential for turning off the transistor (here, alow-level potential) is applied to the wirings GL1 and GL2. Data to bewritten to pixels in the previous row is supplied to the wirings SLR,SLG, SLB, and VL.

<Period T11-T12>

At Time T11, a potential for turning on the transistor (here, ahigh-level potential) is applied to the wirings GL1 and GL2. Inaddition, data potentials D_(R), D_(G), and D_(B) are applied to thewirings SLR, SLG, and SLB, respectively. Furthermore, the resetpotential V_(R) is applied to the wiring VL.

In the period T11-T12, the transistors M1, M3, and M4 are turned on. Thereset potential V_(R) is supplied to an anode electrode of eachlight-emitting element through the transistor M4. In addition, the resetpotential V_(R) is supplied to the second electrode of the capacitor C1through the transistor M3. Furthermore, the data potential D_(R), D_(G),or D_(B) is supplied to the gate of the transistor M2 through thetransistor M1.

At this time, the reset potential V_(R) is applied to the anodeelectrodes of the light-emitting elements ELR, ELG, and ELB. When thereset potential V_(R) is set so that voltage between the pair ofelectrodes of each of the light-emitting elements does not exceed thethreshold voltage, unintended light is not emitted from each of thelight-emitting elements.

<Period T12-T13>

Then, at Time T12, a low-level potential is applied to the wiring GL1, ahigh-level potential is applied to the wiring GL2, and the datapotential D_(W) is applied to the wiring VL.

The transistor M1 is turned off, so that the gate of the transistor M2is brought into a floating state. The potential of the gate of thetransistor M2 can be changed by capacitive coupling when the datapotential D_(W) is applied to the second electrode of the capacitor C1through the transistor M3.

Here, the data potential D_(W) is applied to the subpixels 21R, 21G, and21B. Thus, the emission luminance of the light-emitting elements of thesubpixels 21R, 21G, and 21B can be corrected in a similar manner. Forexample, a high-level potential is applied as the data potential D_(W),so that the emission luminance of the light-emitting elements of thesubpixels 21R, 21G, and 21B can be increased uniformly.

With such a driving method, emission luminance can be adjusted for eachof the pixels 20, so that what is called pixel dimming can be achieved.Luminance is optimally corrected in accordance with an image to bedisplayed, so that high-quality display can be achieved. In addition, ina conventional display device, video data needs to be generated byaddition of data for display and data for correction and needs to besupplied to pixels. In contrast, in one embodiment of the presentinvention, data for display and data for correction can be independentlysupplied, so that a configuration of a driver circuit or the like can besimplified.

In addition, the wiring VL is shared by the plurality of subpixels, sothat the amount of correction data to be supplied to the wiring VL canbe reduced. Accordingly, frame frequency can be increased and powerconsumption can be reduced.

<At and After Time T13>

At Time T13, a low-level potential is applied to the wiring GL2. Thus,operation of writing data to the pixels 20 is completed. After Time T13,writing operation for the next row is performed.

Driving Method Example 2-2

A driving method example that is different from Driving method example2-1 is described below with reference to a timing chart in FIG. 8B.Here, an example in which the driver circuit portion 12 that supplies adata potential to the wirings SLR, SLG, and SLB includes a demultiplexercircuit is described.

The demultiplexer circuit has a function of time-dividing one datasignal to be input and outputting the data signal to a plurality ofwirings. Here, an example in which data potentials are sequentiallysupplied to the wirings SLR, SLG, and SLB from one demultiplexer circuitis described.

<Before Time T21>

Before Time T21, a potential for turning off the transistor (here, alow-level potential) is applied to the wirings GL1 and GL2. Data to bewritten to pixels in the previous row is supplied to the wirings SLR,SLG, SLB, and VL.

<Period T21-T22>

At Time T21, a potential for turning on the transistor (here, ahigh-level potential) is applied to the wirings GL1 and GL2. Inaddition, the data potential D_(R) is applied to the wiring SLR. Data tobe written to the pixels in the previous row is supplied to the wiringsSLG and SLB. Furthermore, the reset potential V_(R) is applied to thewiring VL.

At this time, data to be written to the pixels in the previous rows isapplied to the subpixels 21G and 21B. However, the reset potential V_(R)is applied to the anode electrodes of the light-emitting elements ELGand ELB; thus, when the reset potential V_(R) is set so that voltagebetween the pair of electrodes of each of the light-emitting elementsdoes not exceed the threshold voltage, unintended light is not emittedfrom each of the light-emitting elements. The data potential D_(R) iswritten to the subpixel 21R, and light is not emitted from thelight-emitting element ELR in a similar manner. Accordingly, light isnot emitted from each of the light-emitting elements until the datapotential D_(W) is written to each of the subpixels, so that display ofan unintended image that decreases display quality can be prevented.

<Period T22-T23>

At Time T22, while the potential for turning on the transistor iscontinuously applied to the wirings GL1 and GL2, the data potentialD_(G) is applied to the wiring SLG and is written to the subpixel 21G.At this time, the data potential D_(R) is applied to the wiring SLR, anddata to be written to the pixels in the previous row is supplied to thewiring SLB. Note that also at this time, light is not emitted from thelight-emitting elements ELR, ELG, and ELB.

<Period T23-T24>

At Time T23, while the potential for turning on the transistor iscontinuously applied to the wirings GL1 and GL2, the data potentialD_(B) is applied to the wiring SLB and is written to the subpixel 21B.At this time, the data potential D_(R) is applied to the wiring SLR, andthe data potential D_(G) is applied to the wiring SLG. Note that also atthis time, light is not emitted from the light-emitting elements ELR,ELG, and ELB.

<Period T24-T25>

Then, at Time T24, a low-level potential is applied to the wiring GL1, ahigh-level potential is applied to the wiring GL2, and the datapotential D_(W) is applied to the wiring VL. Thus, the light-emittingelements included in the subpixels can emit light with luminancecorrected by the data potential D_(W).

The above is the description of the example of the driving method.

Note that although the method for driving the pixel 20 is describedhere, a similar driving method can be applied to the pixel 20 a.

Modification Example 2-1

The display device 10 a shown in FIG. 5 has a structure in which onewiring VL is provided for one pixel 20; however, one wiring VL may beconnected to a plurality of pixels 20.

FIG. 9A is a block diagram of a display device 10 b.

In the example of the display device 10 b, one wiring VL is electricallyconnected to all the pixels 20. The reset potential V_(R) and the datapotential D_(W) are applied to the subpixels 21R, 21G, and 21B in aplurality of pixels 20 arranged in a row direction. Thus, correctiondata can be written row by row.

In the display device 10 b, the number of the wirings VL supplied withthe reset potential V_(R) and the data potential D_(W) can besignificantly reduced. Accordingly, a display device with extremely highdefinition can be achieved.

In the case where the area of the display portion 11 a is large or thenumber of pixels 20 arranged in the row direction is large, there mightbe a difference between a potential applied to the pixel 20 that isclose to the wiring VL and a potential applied to the pixel 20 that isfar from the wiring VL due to the influence of the electric resistanceof the wiring VL. Thus, a structure of a display device 10 c shown inFIG. 9B can inhibit such a problem.

The display device 10 c includes a wiring VL1 and a wiring VL2 at bothends of the display portion 11 a. The same signal is output from thedriver circuit portion 12 to the wirings VL1 and VL2. By inputting thesame signals (the reset potential V_(R) and the data potential D_(W)) tothe pixels 20 from both of the ends of the display portion 11 a in thismanner, the above problem can be favorably inhibited.

Note that although the one wiring VL (or the pair of wirings VL1 andVL2) is connected to all the pixels 20 here, one embodiment of thepresent invention is not limited thereto. For example, one wiring VL maybe provided for a plurality of pixels 20. In that case, what is calledlocal dimming in which emission luminance is adjusted for a plurality ofpixels can be achieved.

The above is the description of Structure example 2.

Structure Example 3

A display device according to one embodiment of the present inventionmay have an imaging function in addition to a function of displaying animage. Specifically, a pixel included in the display device can includea light-emitting element and a light-receiving element. An image of atarget object can be captured by light-receiving elements arranged in amatrix. In addition, the light-emitting element can also be used as alight source for imaging by the light-receiving elements, and light thatis emitted from the light-emitting element and is reflected in a targetobject can be detected by the light-receiving elements.

The display device according to one embodiment of the present inventioncan adjust the gradation of each pixel by using the second datapotential (the data potential D_(W)). For example, when thelight-emitting element is used as the light source for imaging, theemission luminance of each light-emitting element can be increased byusing a potential that increases the gradation of the pixel as thesecond data potential. In addition, the display device according to oneembodiment of the present invention can correct the gradation for eachpixel or for multiple pixels; thus, the luminance of only pixels to beused as the light source can be increased.

For example, the display device can be applied to personalauthentication by capturing an image of biological information such as afingerprint or a palm print with the light-receiving elements. Thedisplay device can also be applied to a touch sensor by sensingpositional information of a target object that touches the displayportion. The display device can also be applied to an image scanner bycapturing an image of an object, a printed material, or the like.

More specific examples are described below with reference to drawings.

FIG. 10A is a block diagram of a display device 10 d. The display device10 d includes a display portion 11 b, the driver circuit portion 12, thedriver circuit portion 13, a driver circuit portion 14, a circuitportion 15, and the like.

The display portion 11 b includes a plurality of pixels 30 arranged in amatrix. The pixels 30 each include the subpixels 21R, 21G, and 21B andan imaging pixel 22. The imaging pixel 22 includes a light-receivingelement that functions as a photoelectric conversion element.

The imaging pixel 22 is electrically connected to wirings TX, SE, RS,and WX. The wirings TX, SE, and RS are electrically connected to thedriver circuit portion 14, and the wiring WX is electrically connectedto the circuit portion 15.

The driver circuit portion 14 has a function of generating a signal fordriving the imaging pixel 22 and outputting the signal to the imagingpixel 22 through the wirings SE, TX, and RS. The circuit portion 15 hasa function of receiving a signal output from the imaging pixel 22through the wiring WX and outputting the signal to the outside as imagedata. The circuit portion 15 functions as a read circuit.

In the example of the display device 10 d, a wiring VLR connected to thesubpixel 21R, a wiring VLG connected to the subpixel 21G, and a wiringVLB connected to the subpixel 21B are provided. The wirings VLR, VLG,and VLB are electrically connected to the driver circuit portion 12, anda reset potential and a data potential are supplied to the wirings VLR,VLG, and VLB from the driver circuit portion 12 in different periods.

Note that one wiring VL may be provided for one pixel 30 like a displaydevice 10 e shown in FIG. 10B. In addition, as in Modification example2-1 (FIGS. 9A and 9B), one wiring VL may be connected to a plurality ofpixels 30.

Pixel Configuration Example 3-1

FIG. 11A shows an example of a circuit that can be used for the imagingpixel 22. The imaging pixel 22 includes a transistor M5, a transistorM6, a transistor M7, a transistor M8, a capacitor C3, and alight-receiving element PD.

A gate of the transistor M5 is electrically connected to the wiring TX.One of a source and a drain of the transistor M5 is electricallyconnected to an anode electrode of the light-receiving element PD. Theother of the source and the drain of the transistor M5 is electricallyconnected to one of a source and a drain of the transistor M6, a firstelectrode of the capacitor C3, and a gate of the transistor M7. A gateof the transistor M6 is electrically connected to the wiring RS. Theother of the source and the drain of the transistor M6 is electricallyconnected to a wiring V1. One of a source and a drain of the transistorM7 is electrically connected to a wiring V3. The other of the source andthe drain of the transistor M7 is electrically connected to one of asource and a drain of the transistor M8. A gate of the transistor M8 iselectrically connected to the wiring SE. The other of the source and thedrain of the transistor M8 is electrically connected to the wiring WX. Acathode electrode of the light-receiving element PD is electricallyconnected to the wiring CL. A second electrode of the capacitor C3 iselectrically connected to a wiring V2.

The transistors M5, M6, and M8 function as switches. The transistor M7functions as an amplifier element (an amplifier).

The wirings TX, SE, and RS are supplied with signals for controlling theconduction and non-conduction of the transistors to which the wiringsTX, SE, and RS are connected. The data potential D_(S) is output fromthe imaging pixel 22 to the wiring WX.

Fixed potentials are applied to the wirings V1 and V3. The potentialapplied to the wiring V1 and the potential applied to the wiring V3 canbe selected in accordance with the configuration of the read circuitincluded in the circuit portion 15. Either a fixed potential or two ormore different potentials may be applied to the wiring V2. The wiring CLis the wiring to which a cathode potential is applied. Here, a potentialhigher than the potential of the wiring V1 is applied to the wiring CLso that a reverse bias is applied to the light-receiving element PD.

Note that the transistors may each include a back gate, as shown in FIG.12 . In FIG. 12 , a pair of gates of each transistor is electricallyconnected to each other.

Note that although the pair of gates of each transistor is electricallyconnected to each other in FIG. 12 , one embodiment of the presentinvention is not limited thereto. The imaging pixel 22 may include atransistor in which one of gates is connected to another wiring. Forexample, when one of a pair of gates of a transistor is connected to awiring to which a fixed potential is applied, the stability ofelectrical characteristics can be improved. Alternatively, one of a pairof gates of a transistor may be connected to a wiring to which apotential for controlling the threshold voltage of the transistor isapplied.

Although the example in which the four transistors each include a backgate is shown here, a transistor that includes a back gate and atransistor that does not include a back gate may be used in combination.

Driving Method Example 3-1

An example of a method for driving the imaging pixel 22 is describedbelow with reference to a timing chart in FIG. 11B. FIG. 11B showssignals input to the wirings TX, SE, RS, and WX.

<Before Time T31>

Before Time T31, low-level potentials are applied to the wirings TX, SE,and RS. Data is not output to the wiring WX, and the wiring WX isregarded as being set to a low-level potential here. Note that apredetermined potential may be applied to the wiring WX.

<Period T31-T32>

At Time T31, a potential for turning on the transistor (here, ahigh-level potential) is applied to the wirings TX and RS. In addition,a potential for turning off the transistor (here, a low-level potential)is applied to the wiring SE.

At this time, the transistors M5 and M6 are turned on, so that apotential lower than the potential of the cathode electrode of thelight-receiving element PD is applied to the anode electrode of thelight-receiving element PD from the wiring V1 through the transistors M6and M5. That is, reverse bias voltage is applied to the light-receivingelement PD.

In addition, the potential of the wiring V1 is also supplied to thefirst electrode of the capacitor C3, so that charge is stored in thecapacitor C3.

The period T31-T32 can also be referred to as a reset (initialization)period.

<Period T32-T33>

At Time T32, low-level potentials are applied to the wirings TX and RS.Thus, the transistors M5 and M6 are turned off.

The transistor M5 is turned off, so that the reverse bias voltage isretained in the light-receiving element PD. Here, photoelectricconversion is caused by incident light on the light-receiving elementPD, and charge is accumulated in the anode electrode of thelight-receiving element PD.

The period T32-T33 can also be referred to as an exposure period. Theexposure period is set in accordance with the sensitivity of thelight-receiving element PD, the amount of incident light, or the likeand is preferably set to be much longer than at least a reset period.

In addition, in the period T32-T33, the transistors M5 and M6 are turnedoff, so that the potential of the first electrode of the capacitor C3 isheld at a low-level potential supplied from the wiring V1.

<Period T33-T34>

At Time T33, a high-level potential is applied to the wiring TX. Thus,the transistor M5 is turned on, and the charge accumulated in thelight-receiving element PD is transferred to the first electrode of thecapacitor C3 through the transistor M5. Accordingly, the potential of anode to which the first electrode of the capacitor C3 is connectedbecomes higher in accordance with the amount of charge accumulated inthe light-receiving element PD. Consequently, a potential correspondingto the amount of light to which the light-receiving element PD isexposure is applied to the gate of the transistor M7.

<Period T34-T35>

At Time T34, a low-level potential is applied to the wiring TX. Thus,the transistor M5 is turned off, and a node to which the gate of thetransistor M7 is connected is brought into a floating state. Since thelight-receiving element PD is continuously exposed to light, a change inthe potential of the node to which the gate of the transistor M7 isconnected can be prevented by turning off the transistor M5 after thetransfer operation in the period T33-T34 is completed.

<Period T35-T36>

At Time T35, a high-level potential is applied to the wiring SE. Thus,the transistor M8 is turned on. The period T35-T36 can be referred to asa read period.

For example, a source follower circuit is composed of the transistor M7and a transistor included in the circuit portion 15 so that data can beread. In that case, the data potential D_(S) output to the wiring WX isdetermined in accordance with a gate potential of the transistor M7.Specifically, a potential obtained by subtracting the threshold voltageof the transistor M7 from the gate potential of the transistor M7 isoutput to the wiring WX as the data potential D_(S), and the potentialis read by the read circuit included in the circuit portion 15.

Note that a source ground circuit is composed of the transistor M7 andthe transistor included in the circuit portion 15 so that data can beread by the read circuit included in the circuit portion 15.

<At and After Time T36>

At Time T36, a low-level potential is applied to the wiring SE. Thus,the transistor M8 is turned off. Accordingly, data reading in theimaging pixel 22 is completed. After Time T36, data reading operation issequentially performed in the subsequent rows.

The above is the description of Driving method example 3-1.

Note that as shown in FIG. 13 , a high-level potential may be applied tothe wiring TX in the period T32-T33 that is the exposure period. At thistime, the transistor M5 is on during the exposure period; thus, lightexposure and transfer can be performed at the same time. Thus, theexposure period can be set long or driving frequency can be increased.

When the driving methods shown in FIGS. 11B and 13 are used, theexposure period and the read period can be set independently; therefore,light exposure can be concurrently performed on all the imaging pixels22 in the display portion 11 b, and then data can be sequentially read.Accordingly, what is called global shutter driving can be achieved. Inthe case of performing global shutter driving, a transistor including anoxide semiconductor, which has an extremely low leakage off-statecurrent, is preferably used as a transistor functioning as a switch inthe imaging pixel 22 (in particular, each of the transistors M5 and M6).

The above is the description of Structure example 3.

At least part of this embodiment can be implemented in combination withany of the other embodiments described in this specification asappropriate.

Embodiment 2

In this embodiment, a display device with an imaging function isdescribed. A display device described below includes a light-emittingelement and a light-receiving element. The display device includes afunction of displaying an image, a function of performing positiondetection with reflected light from an object to be detected, and afunction of performing capturing an image of a fingerprint or the likewith reflected light from an object to be detected. The display devicedescribed below can also be regarded to have a function of a touch paneland a function of a fingerprint sensor.

A display device according to one embodiment of the present inventionincludes a light-emitting element emitting first light (a light-emittingdevice) and a light-receiving element receiving the first light (alight-receiving device). That is, the light-receiving element is anelement whose light-receiving wavelength range covers an emissionwavelength of the light-emitting element. The light-receiving element ispreferably a photoelectric conversion element. As the first light,visible light or infrared light can be used. In the case where infraredlight is used as the first light, in addition to the light-emittingelement emitting the first light, a light-emitting element emittingvisible light can be included.

In addition, the display device includes a pair of substrates (alsoreferred to as a first substrate and a second substrate). Thelight-emitting element and the light-receiving element are positionedbetween the first substrate and the second substrate. The firstsubstrate is positioned on a display surface side, and the secondsubstrate is positioned on a side opposite to the display surface side.

Visible light is emitted from the light-emitting element to the outsidethrough the first substrate. The plurality of light-emitting elementsarranged in a matrix are included in the display device, so that animage can be displayed.

The first light emitted from the light-emitting element reaches asurface of the first substrate. Here, when an object touches the surfaceof the first substrate, the first light is scattered at an interfacebetween the first substrate and the object, and then part of thescattered light is incident on the light-receiving element. When thelight-receiving element receives the first light, the light-receivingelement can convert the first light into an electric signal inaccordance with the intensity of the first light and output the electricsignal. In the case where a plurality of light-receiving elementsarranged in a matrix are included in the display device, positionaldata, shape, or the like of the object that touches the first substratecan be detected. That is, the display device can function as an imagesensor panel, a touch sensor panel, or the like.

Note that even in the case where the object does not touch the surfaceof the first substrate, the first light that has passed the firstsubstrate is reflected or scattered in the surface of the object, andreflected light or scattered light is incident on the light-receivingelement through the first substrate. Thus, the display device can alsobe used as a non-contact touch sensor panel (also referred to as anear-touch panel).

In the case where visible light is used as the first light, the firstlight used for image display can be used as a light source of a touchsensor. In that case, the light-emitting element has a function of adisplay element and a function of a light source, so that the structureof the display device can be simplified. In contrast, in the case whereinfrared light is used as the first light, a user does not perceive theinfrared light, so that imaging or sensing can be performed by thelight-receiving element without a reduction in visibility of a displayimage.

In the case where infrared light is used as the first light, infraredlight, preferably near-infrared light is used. In particular,near-infrared light having one or more peaks in the range of awavelength of greater than or equal to 700 nm and less than or equal to2500 nm can be favorably used. In particular, the use of light havingone or more peaks in the range of a wavelength of greater than or equalto 750 nm and less than or equal to 1000 nm is preferable because itpermits an extensive choice of a material used for an active layer ofthe light-receiving element.

When a fingertip touches a surface of the display device, the image of ashape of a fingerprint can be captured. The fingerprint has a projectionand a depression. The first light is likely to be scattered in theprojection of the fingerprint that touches the surface of the firstsubstrate. Therefore, the intensity of scattered light that is incidenton the light-receiving element overlapping with the projection of thefingerprint is high and the intensity of scattered light that isincident on the light-receiving element overlapping with the depressionof the fingerprint is low. Accordingly, the image of the fingerprint canbe captured. A device including a display device according to oneembodiment of the present invention can perform fingerprintauthentication that is a kind of biological authentication by utilizinga captured fingerprint image.

In addition, the display device can also capture the image of a bloodvessel, especially a vein of a finger, a hand, or the like. For example,light having a wavelength of 760 nm and its vicinity is not absorbed byreduced hemoglobin in the vein, so that the position of the vein can bedetected by making an image from reflected light from a palm, a finger,or the like that is received by the light-receiving element. A deviceincluding a display device according to one embodiment of the presentinvention can perform vein authentication that is a kind of biologicalauthentication by utilizing a captured vein image.

In addition, the device including a display device according to oneembodiment of the present invention can perform touch sensing,fingerprint authentication, and vein authentication at the same time.Thus, high-security biological authentication can be performed at lowcost without increasing the number of components.

The light-receiving element is preferably an element capable ofreceiving visible light and infrared light. In that case, thelight-emitting element preferably includes a light-emitting elementemitting infrared light and a light-emitting element emitting visiblelight. Accordingly, visible light is reflected by a user's finger andreflected light is received by the light-receiving element, so that theimage of a shape of a fingerprint can be captured. Furthermore, theimage of a shape of a vein can be captured with infrared light.Accordingly, both fingerprint authentication and vein authentication canbe performed in one display device. Moreover, fingerprint imaging andvein imaging may be performed either at different timings or at the sametime. In the case where fingerprint imaging and vein imaging areperformed at the same time, image data including both data on afingerprint shape and data on a vein shape can be obtained, so thatbiological authentication with higher accuracy can be achieved.

Alternatively, the display device according to one embodiment of thepresent invention may have a function of detecting a user's healthcondition. For example, by utilizing changes in reflectance andtransmittance with respect to visible light and infrared light inaccordance with a change in blood oxygen saturation and obtaining a timechange in the oxygen saturation, a heart rate can be measured.Furthermore, a glucose concentration in dermis, a neutral fatsconcentration in the blood, or the like can also be measured by infraredlight or visible light. The device including the display deviceaccording to one embodiment of the present invention can be used as ahealth care device capable of obtaining index data on a user's healthcondition.

A sealing substrate for sealing the light-emitting element, a protectivefilm, or the like can be used for the first substrate. In addition, aresin layer may be provided between the first substrate and the secondsubstrate to attach the first substrate and the second substrate to eachother.

Here, as the light-emitting element, an EL element such as an organiclight-emitting diode (OLED) or a quantum-dot light-emitting diode (QLED)is preferably used. As a light-emitting substance of the EL element, asubstance emitting fluorescence (a fluorescent material), a substanceemitting phosphorescence (a phosphorescent material), a substanceexhibiting thermally activated delayed fluorescence (a thermallyactivated delayed fluorescent (TADF) material), an inorganic compound(e.g., a quantum dot material), or the like can be used. Alternatively,an LED such as a micro-LED can be used as the light-emitting element.

As the light-receiving device, a PN photodiode or a PIN photodiode canbe used, for example. The light-receiving element functions as aphotoelectric conversion element that detects light incident on thelight-receiving element and generates charge. The amount of generatedcharge in the photoelectric conversion element is determined dependingon the amount of incident light. It is particularly preferable to use anorganic photodiode including a layer containing an organic compound asthe light-receiving element. An organic photodiode, which is easily madethin, lightweight, and large in area and has a high degree of freedomfor shape and design, can be used in a variety of display devices.

The light-emitting element can have a stacked-layer structure includinga light-emitting layer between a pair of electrodes, for example. Thelight-receiving element can have a stacked-layer structure including anactive layer between the pair of electrodes. A semiconductor materialcan be used for the active layer of the light-receiving element. Forexample, an inorganic semiconductor material such as silicon can beused.

An organic compound is preferably used for the active layer of thelight-receiving element. In that case, the light-emitting element andone electrode (also referred to as a pixel electrode) of thelight-receiving element are preferably provided on the same plane. Inaddition, the light-emitting element and the other electrode of thelight-receiving element are further preferably formed using onecontinuous conductive layer (also referred to as a common electrode).Furthermore, it is still further preferable that the light-emittingelement and the light-receiving element include a common layer. Thus,the manufacturing process of the light-emitting element and thelight-receiving element can be simplified, so that the manufacturingcost can be reduced and the manufacturing yield can be increased.

More specific examples are described below with reference to drawings.

Structure Example 1 of Display Panel Structure Example 1-1

FIG. 14A is a schematic diagram of a display panel 50. The display panel50 includes a substrate 51, a substrate 52, a light-receiving element53, a light-emitting element 57R, a light-emitting element 57G, alight-emitting element 57B, a functional layer 55, and the like.

The light-emitting elements 57R, 57G, and 57B and the light-receivingelement 53 are provided between the substrate 51 and the substrate 52.

The light-emitting elements 57R, 57G, and 57B emit red (R) light, green(G) light, and blue (B) light, respectively.

The display panel 50 includes a plurality of pixels arranged in amatrix. One pixel includes at least one subpixel. One subpixel includesone light-emitting element. For example, the pixel can include threesubpixels (e.g., three colors of R, G, and B or three colors of yellow(Y), cyan (C), and magenta (M)) or four subpixels (e.g., four colors ofR, G, B, and white (W) or four colors of R, G, B, and Y). The pixelfurther includes the light-receiving element 53. The light-receivingelement 53 may be provided in all the pixels or in some of the pixels.In addition, one pixel may include a plurality of light-receivingelements 53.

FIG. 14A shows a state where a finger 60 touches a surface of thesubstrate 52. Part of light emitted from the light-emitting element 57Gis reflected or scattered in a contact portion of the substrate 52 andthe finger 60. In the case where part of reflected light or scatteredlight is incident on the light-receiving element 53, the contact of thefinger 60 with the substrate 52 can be detected. That is, the displaypanel 50 can function as a touch panel.

The functional layer 55 includes a circuit for driving thelight-emitting elements 57R, 57G, and 57B, and a circuit for driving thelight-receiving element 53. The functional layer 55 includes a switch, atransistor, a capacitor, a wiring, and the like. Note that in the casewhere the light-emitting elements 57R, 57G, and 57B and thelight-receiving element 53 are driven by a passive-matrix method, thefunctional layer 55 does not necessarily include a switch or atransistor.

The display panel 50 may have a function of detecting a fingerprint ofthe finger 60. FIG. 14B schematically shows an enlarged view of thecontact portion when the finger 60 touches the substrate 52. FIG. 14Bshows light-emitting elements 57 and the light-receiving elements 53that are alternately arranged.

The fingerprint of the finger 60 is formed of depressions andprojections. Therefore, as shown in FIG. 14B, the projections of thefingerprint touch the substrate 52, and scattered light (indicated bydashed-dotted arrows) occurs on surfaces where the projections of thefingerprint touch the substrate 52.

As shown in FIG. 14B, in the intensity distribution of the scatteredlight on the surface where the finger 60 touches the substrate 52, theintensity of light almost perpendicular to the contact surface is thehighest, and the intensity of light becomes lower as an angle becomeslarger in an oblique direction. Thus, the intensity of light received bythe light-receiving element 53 positioned directly below the contactsurface (i.e., positioned in a portion overlapping with the contactsurface) is the highest. Scattered light at greater than or equal to apredetermined scattering angle is fully reflected in the other surface(a surface opposite to the contact surface) of the substrate 52 and doesnot pass through the light-receiving element 53. As a result, a clearfingerprint image can be captured.

In the case where an arrangement interval between the light-receivingelements 53 is smaller than a distance between two projections of thefingerprint, preferably a distance between a depression and a projectionadjacent to each other, a clear fingerprint image can be obtained. Adistance between a depression and a projection of a human's fingerprintis approximately 200 μm; thus, the arrangement interval between thelight-receiving elements 53 is, for example, less than or equal to 400μm, preferably less than or equal to 200 μm, further preferably lessthan or equal to 150 μm, still further preferably less than or equal to100 μm, even still further preferably less than or equal to 50 μm andgreater than or equal to 1 μm, preferably greater than or equal to 10μm, further preferably greater than or equal to 20 μm.

FIG. 14C shows an example of a fingerprint image captured with thedisplay panel 50. In FIG. 14C, in an imaging range 63, the outline ofthe finger 60 is indicated by a dashed-dotted line and the outline of acontact portion 61 is indicated by a dashed line. In the contact portion61, the image of a high-contrast fingerprint 62 can be captured by adifference in light incident on the light-receiving element 53.

The display panel 50 can also function as a touch panel or a pen tablet.FIG. 14D shows a state in which a tip of a stylus 65 slides in adirection indicated by a dashed-dotted arrow while the tip of the stylus65 touches the substrate 52.

As shown in FIG. 14D, when light scattered in the tip of the stylus 65and the contact surface of the substrate 52 is incident on thelight-receiving element 53 that overlaps with the contact surface, theposition of the tip of the stylus 65 can be detected with high accuracy.

FIG. 14E shows an example of a path 66 of the stylus 65 that is detectedin the display panel 50. The display panel 50 can detect the position ofan object to be detected, such as the stylus 65, with high accuracy, sothat high-definition drawing can be performed using a drawingapplication or the like. Unlike the case of using a capacitive touchsensor, an electromagnetic induction touch pen, or the like, the displaypanel 50 can detect even the position of a highly insulating object tobe detected, the material of a tip portion of the stylus 65 is notlimited, and a variety of writing materials (e.g., a brush, a glass pen,a quill pen, and the like) can be used.

Here, FIGS. 14F to 14H show examples of pixels that can be used for thedisplay panel 50.

Pixels shown in FIGS. 14F and 14G include the light-emitting elements57R, 57G, and 57G for red (R), green (G), and blue (B), respectively,and the light-receiving element 53. The pixels each include a pixelcircuit for driving the light-emitting elements 57R, 57G, and 57B andthe light-receiving element 53.

FIG. 14F shows an example in which three light-emitting elements and onelight-receiving element are provided in a matrix of 2×2. FIG. 14G showsan example in which three light-emitting elements are arranged in onecolumn and one laterally long light-receiving element 53 is providedbelow the three light-emitting elements.

The pixel shown in FIG. 14H includes a light-emitting element 57W forwhite (W). Here, four light-emitting elements are arranged in one columnand the light-receiving element 53 is provided below the fourlight-emitting elements.

Note that the pixel configuration is not limited to the aboveconfiguration, and a variety of pixel arrangements can be employed.

Structure Example 1-2

An example of a structure including a light-emitting element emittingvisible light, a light-emitting element emitting infrared light, and alight-receiving element is described below.

A display panel 50A shown in FIG. 15A includes a light-emitting element571R in addition to the components shown in FIG. 14A. The light-emittingelement 571R is a light-emitting element emitting infrared light IR.Moreover, in that case, an element capable of receiving at least theinfrared light IR emitted from the light-emitting element 571R ispreferably used as the light-receiving element 53. As thelight-receiving element 53, an element capable of receiving visiblelight and infrared light is further preferably used.

As shown in FIG. 15A, when the finger 60 touches the substrate 52, theinfrared light IR emitted from the light-emitting element 57IR isreflected or scattered by the finger 60 and part of reflected light orscattered light is incident on the light-receiving element 53, so thatthe positional information of the finger 60 can be obtained.

FIGS. 15B to 15D show examples of pixels that can be used for thedisplay panel 50A.

FIG. 15B shows an example in which three light-emitting elements arearranged in one column and the light-emitting element 57IR and thelight-receiving element 53 are arranged below the three light-emittingelements in a horizontal direction. FIG. 15C shows an example in whichfour light-emitting elements including the light-emitting element 57IRare arranged in one column and the light-receiving element 53 isprovided below the four light-emitting elements.

FIG. 15D shows an example in which three light-emitting elements and thelight-receiving element 53 arranged in all directions with thelight-emitting element 57IR used as a center.

Note that in the pixels shown in FIGS. 15B to 15D, the positions of thelight-emitting elements can be interchangeable, or the positions of thelight-emitting element and the light-receiving element can beinterchangeable.

The above is the description of Structure example 1 of display panel.

Structure Example 2 of Display Panel Structure Example 2-1

FIG. 16A is a schematic cross-sectional view of a display panel 100A.

The display panel 100A includes a light-receiving element 110 and alight-emitting element 190. The light-receiving element 110 includes apixel electrode 111, a common layer 112, an active layer 113, a commonlayer 114, and a common electrode 115. The light-emitting element 190includes a pixel electrode 191, the common layer 112, a light-emittinglayer 193, the common layer 114, and the common electrode 115.

The pixel electrode 111, the pixel electrode 191, the common layer 112,the active layer 113, the light-emitting layer 193, the common layer114, and the common electrode 115 may each have a single-layer structureor a stacked-layer structure.

The pixel electrode 111 and the pixel electrode 191 are positioned overan insulating layer 214. The pixel electrode 111 and the pixel electrode191 can be formed using the same material in the same step.

The common layer 112 is positioned over the pixel electrode 111 and thepixel electrode 191. The common layer 112 is shared by thelight-receiving element 110 and the light-emitting element 190.

The active layer 113 overlaps with the pixel electrode 111 with thecommon layer 112 therebetween. The light-emitting layer 193 overlapswith the pixel electrode 191 with the common layer 112 therebetween. Theactive layer 113 includes a first organic compound, and thelight-emitting layer 193 includes a second organic compound that isdifferent from the first organic compound.

The common layer 114 is positioned over the common layer 112, the activelayer 113, and the light-emitting layer 193. The common layer 114 isshared by the light-receiving element 110 and the light-emitting element190.

The common electrode 115 includes a portion overlapping with the pixelelectrode 111 with the common layer 112, the active layer 113, and thecommon layer 114 therebetween. The common electrode 115 further includesa portion overlapping with the pixel electrode 191 with the common layer112, the light-emitting layer 193, and the common layer 114therebetween. The common electrode 115 is shared by the light-receivingelement 110 and the light-emitting element 190.

In the display panel of this embodiment, an organic compound is used forthe active layer 113 of the light-receiving element 110. In thelight-receiving element 110, the layers other than the active layer 113can be common to the layers in the light-emitting element 190 (the ELelement). Therefore, the light-receiving element 110 can be formedconcurrently with the formation of the light-emitting element 190 onlyby adding a step of depositing the active layer 113 in the manufacturingprocess of the light-emitting element 190. The light-emitting element190 and the light-receiving element 110 can be formed over onesubstrate. Accordingly, the light-receiving element 110 can beincorporated in the display panel without a significant increase in thenumber of manufacturing steps.

The display panel 100A shows an example in which the light-receivingelement 110 and the light-emitting element 190 have a common structureexcept that the active layer 113 of the light-receiving element 110 andthe light-emitting layer 193 of the light-emitting element 190 areseparately formed. Note that the structures of the light-receivingelement 110 and the light-emitting element 190 are not limited thereto.The light-receiving element 110 and the light-emitting element 190 mayinclude a separately formed layer other than the active layer 113 andthe light-emitting layer 193 (see display panels 100D, 100E, and 100F tobe described later). The light-receiving element 110 and thelight-emitting element 190 preferably include at least one layer used incommon (common layer). Thus, the light-receiving element 110 can beincorporated in the display panel without a significant increase in thenumber of manufacturing steps.

The display panel 100A includes the light-receiving element 110, thelight-emitting element 190, a transistor 131, a transistor 132, and thelike between a pair of substrates (a substrate 151 and a substrate 152).

In the light-receiving element 110, the common layer 112, the activelayer 113, and the common layer 114 that are positioned between thepixel electrode 111 and the common electrode 115 can each be referred toas an organic layer (a layer containing an organic compound). The pixelelectrode 111 preferably has a function of reflecting visible light. Anend portion of the pixel electrode 111 is covered with a partition 216.The common electrode 115 has a function of transmitting visible light.

The light-receiving element 110 has a function of detecting light.Specifically, the light-receiving element 110 is a photoelectricconversion element that receives light 122 entering from the outsidethrough the substrate 152 and converts the light 122 into an electricalsignal.

A light-blocking layer BM is provided on a surface of the substrate 152on the substrate 151 side. The light-blocking layer BM has an opening ata position overlapping with the light-receiving element 110 and anopening at a position overlapping with the light-emitting element 190.Providing the light-blocking layer BM can control the range where thelight-receiving element 110 detects light.

For the light-blocking layer BM, a material that blocks light emittedfrom the light-emitting element can be used. The light-blocking layer BMpreferably absorbs visible light. As the light-blocking layer BM, ablack matrix can be formed using a metal material or a resin materialcontaining pigment (e.g., carbon black) or dye, for example. Thelight-blocking layer BM may have a stacked-layer structure of a redcolor filter, a green color filter, and a blue color filter.

Here, part of light emitted from the light-emitting element 190 isreflected in the display panel 100A and is incident on thelight-receiving element 110 in some cases. The light-blocking layer BMcan reduce the influence of such stray light. For example, in the casewhere the light-blocking layer BM is not provided, light 123 a emittedfrom the light-emitting element 190 is reflected by the substrate 152and reflected light 123 b is incident on the light-receiving element 110in some cases. Providing the light-blocking layer BM can inhibit entryof the reflected light 123 b into the light-receiving element 110.Consequently, noise can be reduced, and the sensitivity of a sensorusing the light-receiving element 110 can be increased.

In the light-emitting element 190, the common layer 112, thelight-emitting layer 193, and the common layer 114 that are positionedbetween the pixel electrode 191 and the common electrode 115 can each bereferred to as an EL layer. The pixel electrode 191 preferably has afunction of reflecting visible light. An end portion of the pixelelectrode 191 is covered with the partition 216. The pixel electrode 111and the pixel electrode 191 are electrically insulated from each otherby the partition 216. The common electrode 115 has a function oftransmitting visible light.

The light-emitting element 190 has a function of emitting visible light.Specifically, the light-emitting element 190 is an electroluminescentlight-emitting element that emits light 121 toward the substrate 152when voltage is applied between the pixel electrode 191 and the commonelectrode 115.

It is preferable that the light-emitting layer 193 be formed not tooverlap with a light-receiving region of the light-receiving element110. Accordingly, it is possible to inhibit the light-emitting layer 193from absorbing the light 122, so that the amount of light with which thelight-receiving element 110 is irradiated can be increased.

The pixel electrode 111 is electrically connected to a source or a drainof the transistor 131 through an opening provided in the insulatinglayer 214. The end portion of the pixel electrode 111 is covered withthe partition 216.

The pixel electrode 191 is electrically connected to a source or a drainof the transistor 132 through an opening provided in the insulatinglayer 214. The end portion of the pixel electrode 191 is covered withthe partition 216. The transistor 132 has a function of controllingdriving of the light-emitting element 190.

The transistor 131 and the transistor 132 are on and in contact with thesame layer (the substrate 151 in FIG. 16A).

At least part of a circuit electrically connected to the light-receivingelement 110 is preferably formed using the same material in the samesteps as a circuit electrically connected to the light-emitting element190. Thus, the thickness of the display panel can be reduced and themanufacturing process can be simplified compared to the case where thetwo circuits are separately formed.

The light-receiving element 110 and the light-emitting element 190 arepreferably covered with a protective layer 195. In FIG. 16A, theprotective layer 195 is provided on and in contact with the commonelectrode 115. Providing the protective layer 195 can inhibit entry ofimpurities such as water into the light-receiving element 110 and thelight-emitting element 190, so that the reliability of thelight-receiving element 110 and the light-emitting element 190 can beincreased. The protective layer 195 and the substrate 152 are attachedto each other with an adhesive layer 142.

Note that as shown in FIG. 17A, the protective layer is not necessarilyprovided over the light-receiving element 110 and the light-emittingelement 190. In FIG. 17A, the common electrode 115 and the substrate 152are attached to each other with the adhesive layer 142.

As shown in FIG. 17B, the light-blocking layer BM is not necessarilyprovided. This structure can increase the light-receiving area of thelight-receiving element 110, so that the sensitivity of the sensor canbe further increased.

Structure Example 2-2

FIG. 16B is a cross-sectional view of a display panel 100B. Note that inthe following description of display panels, the description ofcomponents similar to those of the above display panel might be omitted.

The display panel 100B shown in FIG. 16B includes a lens 149 in additionto the components of the display panel 100A.

The lens 149 is provided at a position overlapping with thelight-receiving element 110. In the display panel 100B, the lens 149 isprovided in contact with the substrate 152. The lens 149 included in thedisplay panel 100B is a convex lens having a convex surface on thesubstrate 151 side. Note that convex lens having a convex surface on thesubstrate 152 side may be provided in a region overlapping with thelight-receiving element 110.

In the case where the light-blocking layer BM and the lens 149 areformed on the same plane of the substrate 152, their formation order isnot limited. FIG. 16B shows an example in which the lens 149 is formedfirst; alternatively, the light-blocking layer BM may be formed first.In FIG. 16B, an end portion of the lens 149 is covered with thelight-blocking layer BM.

In the display panel 100B, the light 122 is incident on thelight-receiving element 110 through the lens 149. With the lens 149, theamount of the light 122 incident on the light-receiving element 110 canbe increased compared to the case where the lens 149 is not provided.This can increase the sensitivity of the light-receiving element 110.

As a method for forming the lens used in the display panel of thisembodiment, a lens such as a microlens may be formed directly over thesubstrate or the light-receiving element, or a lens array formedseparately, such as a microlens array, may be attached to the substrate.

Structure Example 2-3

FIG. 16C is a schematic cross-sectional view of a display panel 100C.The display panel 100C differs from the display panel 100A in that thesubstrate 151, the substrate 152, and the partition 216 are not includedand a substrate 153, a substrate 154, an adhesive layer 155, aninsulating layer 212, and a partition 217 are included.

The substrate 153 and the insulating layer 212 are attached to eachother with the adhesive layer 155. The substrate 154 and the protectivelayer 195 are attached to each other with the adhesive layer 142.

The display panel 100C is formed in such a manner that the insulatinglayer 212, the transistor 131, the transistor 132, the light-receivingelement 110, the light-emitting element 190, and the like that areformed over a formation substrate are transferred onto the substrate153. The substrate 153 and the substrate 154 are preferably flexible.Accordingly, the display panel 100C can be highly flexible. For example,a resin is preferably used for each of the substrate 153 and thesubstrate 154.

For each of the substrate 153 and the substrate 154, any of thefollowing can be used, for example: polyester resins such aspolyethylene terephthalate (PET) and polyethylene naphthalate (PEN), apolyacrylonitrile resin, an acrylic resin, a polyimide resin, apolymethyl methacrylate resin, a polycarbonate (PC) resin, apolyethersulfone (PES) resin, polyamide resins (e.g., nylon and aramid),a polysiloxane resin, a cycloolefin resin, a polystyrene resin, apolyamide-imide resin, a polyurethane resin, a polyvinyl chloride resin,a polyvinylidene chloride resin, a polypropylene resin, apolytetrafluoroethylene (PTFE) resin, an ABS resin, and cellulosenanofiber. Glass that is thin enough to have flexibility may be used forone or both of the substrate 153 and the substrate 154.

For the substrate included in the display panel of this embodiment, afilm having high optical isotropy may be used. Examples of the filmhaving high optical isotropy include a triacetyl cellulose (TAC, alsoreferred to as cellulose triacetate) film, a cycloolefin polymer (COP)film, a cycloolefin copolymer (COC) film, and an acrylic film.

The partition 217 preferably absorbs light emitted from thelight-emitting element. As the partition 217, a black matrix can beformed using a resin material containing pigment or dye, for example.Moreover, the partition 217 can be formed of a colored insulating layerby using a brown resist material.

In the case where the partition 217 is formed using a material thattransmits light emitted from the light-emitting element 190, light 123 cemitted from the light-emitting element 190 might be reflected by thesubstrate 154 and the partition 217 and reflected light 123 d might beincident on the light-receiving element 110. In other cases, the light123 c passes through the partition 217 and is reflected by a transistor,a wiring, or the like, and thus reflected light is incident on thelight-receiving element 110. When the partition 217 absorbs the light123 c, the reflected light 123 d can be inhibited from being incident onthe light-receiving element 110. Consequently, noise can be reduced, andthe sensitivity of the sensor using the light-receiving element 110 canbe increased.

The partition 217 preferably absorbs at least a wavelength of light thatis detected by the light-receiving element 110. For example, in the casewhere the light-receiving element 110 detects red light emitted from thelight-emitting element 190, the partition 217 preferably absorbs atleast red light. For example, when the partition 217 includes a bluecolor filter, the partition 217 can absorb the red light 123 c and thusthe reflected light 123 d can be inhibited from being incident on thelight-receiving element 110.

Structure Example 2-4

Although the light-emitting element and the light-receiving elementinclude two common layers in the above example, one embodiment of thepresent invention is not limited thereto. Examples in which commonlayers have different structures are described below.

FIG. 18A is a schematic cross-sectional view of the display panel 100D.The display panel 100D differs from the display panel 100A in that thecommon layer 114 is not included and a buffer layer 184 and a bufferlayer 194 are included. The buffer layer 184 and the buffer layer 194may each have a single-layer structure or a stacked-layer structure.

In the display panel 100D, the light-receiving element 110 includes thepixel electrode 111, the common layer 112, the active layer 113, thebuffer layer 184, and the common electrode 115. In the display panel100D, the light-emitting element 190 includes the pixel electrode 191,the common layer 112, the light-emitting layer 193, the buffer layer194, and the common electrode 115.

In the display panel 100D, an example is shown in which the buffer layer184 between the common electrode 115 and the active layer 113 and thebuffer layer 194 between the common electrode 115 and the light-emittinglayer 193 are formed separately. As the buffer layer 184 and the bufferlayer 194, one or both of an electron-injection layer and anelectron-transport layer can be formed, for example.

FIG. 18B is a schematic cross-sectional view of the display panel 100E.The display panel 100E differs from the display panel 100A in that thecommon layer 112 is not included and a buffer layer 182 and a bufferlayer 192 are included. The buffer layer 182 and the buffer layer 192may each have a single-layer structure or a stacked-layer structure.

In the display panel 100E, the light-receiving element 110 includes thepixel electrode 111, the buffer layer 182, the active layer 113, thecommon layer 114, and the common electrode 115. In the display panel100E, the light-emitting element 190 includes the pixel electrode 191,the buffer layer 192, the light-emitting layer 193, the common layer114, and the common electrode 115.

In the display panel 100E, an example is shown in which the buffer layer182 between the pixel electrode 111 and the active layer 113 and thebuffer layer 192 between the pixel electrode 191 and the light-emittinglayer 193 are formed separately. As the buffer layer 182 and the bufferlayer 192, one or both of a hole-injection layer and a hole-transportlayer can be formed, for example.

FIG. 18C is a schematic cross-sectional view of the display panel 100F.The display panel 100F differs from the display panel 100A in that thecommon layers 112 and 114 are not included and the buffer layers 182,184, 192, and 194 are included.

In the display panel 100F, the light-receiving element 110 includes thepixel electrode 111, the buffer layer 182, the active layer 113, thebuffer layer 184, and the common electrode 115. In the display panel100F, the light-emitting element 190 includes the pixel electrode 191,the buffer layer 192, the light-emitting layer 193, the buffer layer194, and the common electrode 115.

Another layer as well as the active layer 113 and the light-emittinglayer 193 can be formed separately when the light-receiving element 110and the light-emitting element 190 are manufactured.

In the example of the display panel 100F, in each of the light-receivingelement 110 and the light-emitting element 190, a common layer is notprovided between the pair of electrodes (the pixel electrode 111 or 191and the common electrode 115). The light-receiving element 110 and thelight-emitting element 190 included in the display panel 100F can bemanufactured in the following manner: the pixel electrode 111 and thepixel electrode 191 are formed over the insulating layer 214 using thesame material in the same step; the buffer layer 182, the active layer113, and the buffer layer 184 are formed over the pixel electrode 111;the buffer layer 192, the light-emitting layer 193, and the buffer layer194 are formed over the pixel electrode 191; and then, the commonelectrode 115 is formed to cover the buffer layer 184, the buffer layer194, and the like.

Note that the manufacturing order of the stacked-layer structure of thebuffer layer 182, the active layer 113, and the buffer layer 184 and thestacked-layer structure of the buffer layer 192, the light-emittinglayer 193, and the buffer layer 194 is not particularly limited. Forexample, after the buffer layer 182, the active layer 113, and thebuffer layer 184 are deposited, the buffer layer 192, the light-emittinglayer 193, and the buffer layer 194 may be deposited. In contrast, thebuffer layer 192, the light-emitting layer 193, and the buffer layer 194may be deposited before the buffer layer 182, the active layer 113, andthe buffer layer 184 are deposited. Alternatively, the buffer layer 182,the buffer layer 192, the active layer 113, and the light-emitting layer193 may be deposited in that order, for example.

Structure Example 3 of Display Panel

More specific structure examples of the display panel are describedbelow.

Structure Example 3-1

FIG. 19 is a perspective view of a display panel 200A.

In the display panel 200A, the substrate 151 and the substrate 152 areattached to each other. In FIG. 19 , the substrate 152 is indicated by adashed-dotted line.

The display panel 200A includes a display portion 162, circuits 164, awiring 165, and the like. FIG. 19 shows an example in which anintegrated circuit (IC) 173 and an FPC 172 are mounted on the displaypanel 200A. Thus, the structure shown in FIG. 19 can be regarded as adisplay module including the display panel 200A, the IC, and the FPC.

As the circuits 164, scan line driver circuits can be used.

The wiring 165 has a function of supplying a signal and power to thedisplay portion 162 and the circuits 164. The signal and power are inputto the wiring 165 from the outside through the FPC 172 or from the IC173.

FIG. 19 shows an example in which the IC 173 is provided over thesubstrate 151 by a chip on glass (COG) method, a chip on film (COF)method, or the like. An IC including a scan line driver circuit, asignal line driver circuit, or the like can be used as the IC 173, forexample. Note that the display panel 200A and the display module are notnecessarily provided with an IC. The IC may be mounted on the FPC by aCOF method or the like.

FIG. 20 shows an example of cross sections of part of a region includingthe FPC 172, part of a region including the circuit 164, part of aregion including the display portion 162, and part of a region includingan end portion of the display panel 200A shown in FIG. 19 .

The display panel 200A shown in FIG. 20 includes a transistor 201, atransistor 205, a transistor 206, the light-emitting element 190, thelight-receiving element 110, and the like between the substrate 151 andthe substrate 152.

The substrate 152 and the insulating layer 214 are attached to eachother with the adhesive layer 142. A solid sealing structure, a hollowsealing structure, or the like can be employed to seal thelight-emitting element 190 and the light-receiving element 110. In FIG.20 , a hollow sealing structure is employed in which a space 143surrounded by the substrate 152, the adhesive layer 142, and theinsulating layer 214 is filled with an inert gas (e.g., nitrogen orargon). The adhesive layer 142 may overlap with the light-emittingelement 190. The space 143 surrounded by the substrate 152, the adhesivelayer 142, and the insulating layer 214 may be filled with a resindifferent from that of the adhesive layer 142.

The light-emitting element 190 has a stacked-layer structure in whichthe pixel electrode 191, the common layer 112, the light-emitting layer193, the common layer 114, and the common electrode 115 are stacked inthat order from the insulating layer 214 side. The pixel electrode 191is connected to a conductive layer 222 b included in the transistor 206through an opening provided in the insulating layer 214. The transistor206 has a function of controlling the driving of the light-emittingelement 190. The end portion of the pixel electrode 191 is covered withthe partition 216. The pixel electrode 191 contains a material thatreflects visible light, and the common electrode 115 contains a materialthat transmits visible light.

The light-receiving element 110 has a stacked-layer structure in whichthe pixel electrode 111, the common layer 112, the active layer 113, thecommon layer 114, and the common electrode 115 are stacked in that orderfrom the insulating layer 214 side. The pixel electrode 111 iselectrically connected to the conductive layer 222 b included in thetransistor 205 through an opening provided in the insulating layer 214.The end portion of the pixel electrode 111 is covered with the partition216. The pixel electrode 111 contains a material that reflects visiblelight, and the common electrode 115 contains a material that transmitsvisible light.

Light from the light-emitting element 190 is emitted toward thesubstrate 152. Light is incident on the light-receiving element 110through the substrate 152 and the space 143. For the substrate 152, amaterial having a high visible-light-transmitting property is preferablyused.

The pixel electrode 111 and the pixel electrode 191 can be formed usingthe same material in the same step. The common layer 112, the commonlayer 114, and the common electrode 115 are used in both thelight-receiving element 110 and the light-emitting element 190. Thelight-receiving element 110 and the light-emitting element 190 can havecommon components except the active layer 113 and the light-emittinglayer 193. Thus, the light-receiving element 110 can be incorporated inthe display panel 200A without a significant increase in the number ofmanufacturing steps.

The light-blocking layer BM is provided on the surface of the substrate152 on the substrate 151 side. The light-blocking layer BM has theopening at the position overlapping with the light-receiving element 110and the opening at the position overlapping with the light-emittingelement 190. Providing the light-blocking layer BM can control the rangewhere the light-receiving element 110 detects light. Furthermore,providing the light-blocking layer BM can inhibit light from beingdirectly incident on the light-receiving element 110 from thelight-emitting element 190. Accordingly, a sensor with less noise andhigh sensitivity can be obtained.

The transistor 201, the transistor 205, and the transistor 206 areformed over the substrate 151. These transistors can be formed using thesame material in the same step.

An insulating layer 211, an insulating layer 213, an insulating layer215, and the insulating layer 214 are provided in that order over thesubstrate 151. Part of the insulating layer 211 functions as a gateinsulating layer of each transistor. Part of the insulating layer 213functions as a gate insulating layer of each transistor. The insulatinglayer 215 is provided to cover the transistors. The insulating layer 214is provided to cover the transistors and has a function of aplanarization layer. Note that the number of gate insulating layers andthe number of insulating layers covering the transistors are not limitedand may each be one or two or more.

A material through which impurities such as water and hydrogen do noteasily diffuse is preferably used for at least one of the insulatinglayers covering the transistors. This is because such an insulatinglayer can function as a barrier layer. Such a structure can effectivelyinhibit diffusion of impurities into the transistors from the outsideand increase the reliability of a display device.

An inorganic insulating film is preferably used for each of theinsulating layers 211, 213, and 215. As the inorganic insulating film, asilicon nitride film, a silicon oxynitride film, a silicon oxide film, asilicon nitride oxide film, an aluminum oxide film, or an aluminumnitride film can be used, for example. Alternatively, a hafnium oxidefilm, an yttrium oxide film, a zirconium oxide film, a gallium oxidefilm, a tantalum oxide film, a magnesium oxide film, a lanthanum oxidefilm, a cerium oxide film, a neodymium oxide film, or the like may beused. Alternatively, a stack including two or more of the aboveinsulating films may be used.

Here, an organic insulating film often has a lower barrier property thanan inorganic insulating film. Therefore, the organic insulating filmpreferably has an opening in the vicinity of an end portion of thedisplay panel 200A. This can inhibit entry of impurities from the endportion of the display panel 200A through the organic insulating film.Alternatively, the organic insulating film may be formed so that its endportion is positioned on the inner side compared to the end portion ofthe display panel 200A, to prevent the organic insulating film frombeing exposed at the end portion of the display panel 200A.

An organic insulating film is suitable for the insulating layer 214functioning as a planarization layer. Examples of materials that can beused for the organic insulating film include an acrylic resin, apolyimide resin, an epoxy resin, a polyamide resin, a polyimide-amideresin, a siloxane resin, a benzocyclobutene-based resin, a phenol resin,and precursors of these resins.

In a region 228 shown in FIG. 20 , an opening is formed in theinsulating layer 214. This can inhibit entry of impurities into thedisplay portion 162 from the outside through the insulating layer 214even when an organic insulating film is used as the insulating layer214. Consequently, the reliability of the display panel 200A can beincreased.

The transistors 201, 205, and 206 each include a conductive layer 221functioning as a gate, the insulating layer 211 functioning as a gateinsulating layer, a conductive layer 222 a and the conductive layer 222b functioning as a source and a drain, a semiconductor layer 231, theinsulating layer 213 functioning as a gate insulating layer, and aconductive layer 223 functioning as a gate. Here, a plurality of layersobtained by processing the same conductive film are shown with the samehatching pattern. The insulating layer 211 is positioned between theconductive layer 221 and the semiconductor layer 231. The insulatinglayer 213 is positioned between the conductive layer 223 and thesemiconductor layer 231.

There is no particular limitation on the structure of the transistorsincluded in the display panel of this embodiment. For example, a planartransistor, a staggered transistor, or an inverted staggered transistorcan be used. A top-gate transistor or a bottom-gate transistor can beused. Alternatively, gates may be provided above and below asemiconductor layer where a channel is formed.

The transistors 201, 205, and 206 each have a structure in which thesemiconductor layer where a channel is formed is positioned between twogates. The two gates may be connected to each other and supplied withthe same signal to operate the transistor. Alternatively, the thresholdvoltage of the transistor may be controlled by applying a potential forcontrolling the threshold voltage to one of the two gates and apotential for driving to the other of the two gates.

There is no particular limitation on the crystallinity of asemiconductor material used for the transistors, and any of an amorphoussemiconductor, a single crystal semiconductor, and a semiconductorhaving crystallinity other than single crystal (a microcrystallinesemiconductor, a polycrystalline semiconductor, or a semiconductorpartly including crystal regions) may be used. It is preferable to use asingle crystal semiconductor or a semiconductor having crystallinitybecause degradation of transistor characteristics can be inhibited.

The semiconductor layer of the transistor preferably contains a metaloxide (also referred to as an oxide semiconductor). Alternatively, thesemiconductor layer of the transistor may contain silicon. Examples ofsilicon include amorphous silicon and crystalline silicon (e.g.,low-temperature polysilicon and single crystal silicon).

The semiconductor layer preferably contains indium, M (M is one or morekinds selected from gallium, aluminum, silicon, boron, yttrium, tin,copper, vanadium, beryllium, titanium, iron, nickel, germanium,zirconium, molybdenum, lanthanum, cerium, neodymium, hafnium, tantalum,tungsten, and magnesium), and zinc, for example. Specifically, M ispreferably one or more kinds selected from aluminum, gallium, yttrium,and tin.

It is particularly preferable to use an oxide containing indium (In),gallium (Ga), and zinc (Zn) (also referred to as IGZO) for thesemiconductor layer.

In the case where the semiconductor layer is an In-M-Zn oxide, theatomic ratio of In to M of a sputtering target used for depositing theIn-M-Zn oxide is preferably 1 or more. The atomic ratio of metalelements in such a sputtering target is, for example, In:M:Zn=1:1:1,In:M:Zn=1:1:1.2, In:M:Zn=2:1:3, In:M:Zn=3:1:2, In:M:Zn=4:2:3,In:M:Zn=4:2:4.1, In:M:Zn=5:1:3, In:M:Zn=5:1:6, In:M:Zn=5:1:7,In:M:Zn=5:1:8, In:M:Zn=6:1:6, or In:M:Zn=5:2:5.

A target containing a polycrystalline oxide is preferably used as thesputtering target, which facilitates formation of a semiconductor layerhaving crystallinity. Note that the atomic ratio in the semiconductorlayer to be deposited varies within the range of ±40% from any of theatomic ratios of the metal elements contained in the sputtering target.For example, in the case where the composition of a sputtering targetused for the semiconductor layer is In:Ga:Zn=4:2:4.1 [atomic ratio], thecomposition of the semiconductor layer to be deposited is in theneighborhood of In:Ga:Zn=4:2:3 [atomic ratio] in some cases.

Note that when the atomic ratio is described as In:Ga:Zn=4:2:3 or asbeing in the neighborhood thereof, the case is included where the atomicproportion of Ga is greater than or equal to 1 and less than or equal to3 and the atomic proportion of Zn is greater than or equal to 2 and lessthan or equal to 4 with the atomic proportion of In being 4. Inaddition, when the atomic ratio is described as In:Ga:Zn=5:1:6 or asbeing in the neighborhood thereof, the case is included where the atomicproportion of Ga is greater than 0.1 and less than or equal to 2 and theatomic proportion of Zn is greater than or equal to 5 and less than orequal to 7 with the atomic proportion of In being 5. Furthermore, whenthe atomic ratio is described as In:Ga:Zn=1:1:1 or as being in theneighborhood thereof, the case is included where the atomic proportionof Ga is greater than 0.1 and less than or equal to 2 and the atomicproportion of Zn is greater than 0.1 and less than or equal to 2 withthe atomic proportion of In being 1.

The transistor included in the circuit 164 and the transistor includedin the display portion 162 may have the same structure or differentstructures. One structure or two or more kinds of structures may beemployed for a plurality of transistors included in the circuit 164.Similarly, one structure or two or more kinds of structures may beemployed for a plurality of transistors included in the display portion162.

A connection portion 204 is provided in a region of the substrate 151where the substrate 152 does not overlap. In the connection portion 204,the wiring 165 is electrically connected to the FPC 172 through aconductive layer 166 and a connection layer 242. On a top surface of theconnection portion 204, the conductive layer 166 obtained by processingthe same conductive film as the pixel electrode 191 is exposed. Thus,the connection portion 204 and the FPC 172 can be electrically connectedto each other through the connection layer 242.

A variety of optical members can be arranged on an outer surface of thesubstrate 152. Examples of the optical members include a polarizingplate, a retardation plate, a light diffusion layer (e.g., a diffusionfilm), an anti-reflective layer, and a light-condensing film.Furthermore, an antistatic film inhibiting the attachment of dust, awater-repellent film suppressing the attachment of stain, a hard coatfilm inhibiting generation of a scratch caused by the use, animpact-absorbing layer, or the like may be provided on the outer surfaceof the substrate 152.

For each of the substrates 151 and 152, glass, quartz, ceramic,sapphire, a resin, or the like can be used. When each of the substrates151 and 152 is formed using a flexible material, the flexibility of thedisplay panel can be increased.

As the adhesive layer 142, the adhesive layer 155, and the like, any ofa variety of curable adhesives such as a reactive curable adhesive, athermosetting curable adhesive, an anaerobic adhesive, and aphotocurable adhesive such as an ultraviolet curable adhesive can beused. Examples of these adhesives include an epoxy resin, an acrylicresin, a silicone resin, a phenol resin, a polyimide resin, an imideresin, a polyvinyl chloride (PVC) resin, a polyvinyl butyral (PVB)resin, and an ethylene vinyl acetate (EVA) resin. In particular, amaterial with low moisture permeability, such as an epoxy resin, ispreferred. A two-component-mixture-type resin may be used. An adhesivesheet or the like may be used.

As the connection layer 242, an anisotropic conductive film (ACF), ananisotropic conductive paste (ACP), or the like can be used.

The light-emitting element 190 may be a top emission, bottom emission,or dual emission light-emitting element, or the like. A conductive filmthat transmits visible light is used as the electrode through whichlight is extracted. A conductive film that reflects visible light ispreferably used as the electrode through which light is not extracted.

The light-emitting element 190 includes at least the light-emittinglayer 193. In addition to the light-emitting layer 193, thelight-emitting element 190 may further include a layer containing any ofa substance with a high hole-injection property, a substance with a highhole-transport property, a hole-blocking material, a substance with ahigh electron-transport property, a substance with a highelectron-injection property, a substance with a bipolar property (asubstance with a high electron- and hole-transport property), and thelike. For example, the common layer 112 preferably includes one or bothof a hole-injection layer and a hole-transport layer. For example, thecommon layer 114 preferably includes one or both of anelectron-transport layer and an electron-injection layer.

Either a low-molecular compound or a high-molecular compound can be usedfor the common layer 112, the light-emitting layer 193, and the commonlayer 114, and an inorganic compound may also be contained. The layersincluded in the common layer 112, the light-emitting layer 193, and thecommon layer 114 can be formed by any of the following methods, forexample: an evaporation method (including a vacuum evaporation method),a transfer method, a printing method, an inkjet method, and a coatingmethod.

The light-emitting layer 193 may contain an inorganic compound such asquantum dots.

The active layer 113 of the light-receiving element 110 contains asemiconductor. Examples of the semiconductor include an inorganicsemiconductor such as silicon and an organic semiconductor including anorganic compound. This embodiment shows an example in which an organicsemiconductor is used as the semiconductor contained in the activelayer. The use of an organic semiconductor is preferable because thelight-emitting layer 193 of the light-emitting element 190 and theactive layer 113 of the light-receiving element 110 can be formed by thesame method (e.g., a vacuum evaporation method) and thus the samemanufacturing apparatus can be used.

Examples of an n-type semiconductor material contained in the activelayer 113 include electron-accepting organic semiconductor materialssuch as fullerene (e.g., C₆₀ and C₇₀) and fullerene derivatives.Fullerene has a soccer ball-like shape, which is energetically stable.HOMO and LUMO levels of fullerene are deep (low). Since the LUMO levelof fullerene is deep, fullerene has an extremely high electron-acceptingproperty (acceptor property). In general, when π-electron conjugation(resonance) spreads on a plane like benzene, an electron-donatingproperty (donor property) becomes high. However, since fullerene has aspherical shape, fullerene has a high electron-accepting property evenwhen a π-electron widely spreads. The high electron-accepting propertyis advantageous to a light-receiving device because charge separationcan be efficiently performed at high speed. In addition, C₆₀ and C₇₀each have a wide absorption band in a visible light region, and it isparticularly preferable to use C₇₀ because C₇₀ has a wider π-electronconjugated system than C₆₀ and a wide absorption band also in a longwavelength region.

Other examples of the n-type semiconductor material contained in theactive layer 113 include a metal complex having a quinoline skeleton, ametal complex having a benzoquinoline skeleton, a metal complex havingan oxazole skeleton, a metal complex having a thiazole skeleton, anoxadiazole derivative, a triazole derivative, an imidazole derivative,an oxazole derivative, a thiazole derivative, a phenanthrolinederivative, a quinoline derivative, a benzoquinoline derivative, aquinoxaline derivative, a dibenzoquinoxaline derivative, a pyridinederivative, a bipyridine derivative, a pyrimidine derivative, anaphthalene derivative, an anthracene derivative, a coumarin derivative,a rhodamine derivative, a triazine derivative, and a quinone derivative.

Examples of a p-type semiconductor material contained in the activelayer 113 include electron-donating organic semiconductor materials suchas copper(II) phthalocyanine (CuPc), tetraphenyldibenzoperiflanthene(DBP), zinc phthalocyanine (ZnPc), tin phthalocyanine (SnPc), andquinacridone.

Examples of a p-type semiconductor material include a carbazolederivative, a thiophene derivative, a furan derivative, and a compoundhaving an aromatic amine skeleton. Other examples of the p-typesemiconductor material include a naphthalene derivative, an anthracenederivative, a pyrene derivative, a triphenylene derivative, a fluorenederivative, a pyrrole derivative, a benzofuran derivative, abenzothiophene derivative, an indole derivative, a dibenzofuranderivative, a dibenzothiophene derivative, an indolocarbazolederivative, a porphyrin derivative, a phthalocyanine derivative, anaphthalocyanine derivative, a quinacridone derivative, a polyphenylenevinylene derivative, a polyparaphenylene derivative, a polyfluorenederivative, a polyvinylcarbazole derivative, and a polythiophenederivative.

For example, the active layer 113 is preferably formed by co-evaporationof an n-type semiconductor and a p-type semiconductor. Alternatively,the active layer 113 may be formed by stacking an n-type semiconductorand a p-type semiconductor.

As materials of a gate, a source, and a drain of a transistor, andconductive layers functioning as wirings and electrodes included in thedisplay panel, any of metals such as aluminum, titanium, chromium,nickel, copper, yttrium, zirconium, molybdenum, silver, tantalum, andtungsten, or an alloy containing any of these metals as its maincomponent can be used. A single-layer structure or a stacked-layerstructure including a film containing any of these materials can beused.

As a light-transmitting conductive material, a conductive oxide such asindium oxide, indium tin oxide, indium zinc oxide, zinc oxide, or zincoxide containing gallium, or graphene can be used. Alternatively, ametal material such as gold, silver, platinum, magnesium, nickel,tungsten, chromium, molybdenum, iron, cobalt, copper, palladium, ortitanium, or an alloy material containing any of these metal materialscan be used. Alternatively, a nitride of the metal material (e.g.,titanium nitride) or the like may be used. Note that in the case ofusing the metal material or the alloy material (or the nitride thereof),the thickness is preferably set small enough to transmit light.Alternatively, a stacked film of any of the above materials can be usedfor the conductive layers. For example, a stacked film of indium tinoxide and an alloy of silver and magnesium is preferably used becauseconductivity can be increased. These materials can also be used forconductive layers such as wirings and electrodes included in the displaypanel, and conductive layers (e.g., a conductive layer functioning as apixel electrode or a common electrode) included in a display element.

Examples of insulating materials that can be used for the insulatinglayers include a resin such as an acrylic resin and an epoxy resin, andan inorganic insulating material such as silicon oxide, siliconoxynitride, silicon nitride oxide, silicon nitride, and aluminum oxide.

Structure Example 3-2

FIG. 21A is a cross-sectional view of a display panel 200B. The displaypanel 200B differs from the display panel 200A mainly in that the lens149 and the protective layer 195 are provided.

Providing the protective layer 195 covering the light-receiving element110 and the light-emitting element 190 can inhibit diffusion ofimpurities such as water into the light-receiving element 110 and thelight-emitting element 190, so that the reliability of thelight-receiving element 110 and the light-emitting element 190 can beincreased.

In the region 228 in the vicinity of an end portion of the display panel200B, the insulating layer 215 and the protective layer 195 arepreferably in contact with each other through an opening in theinsulating layer 214. In particular, the inorganic insulating filmincluded in the insulating layer 215 and an inorganic insulating filmincluded in the protective layer 195 are preferably in contact with eachother. Thus, diffusion of impurities from the outside into the displayportion 162 through an organic insulating film can be inhibited.Accordingly, the reliability of the display panel 200B can be increased.

FIG. 21B shows an example in which the protective layer 195 has athree-layer structure. In FIG. 21B, the protective layer 195 includes aninorganic insulating layer 195 a over the common electrode 115, anorganic insulating layer 195 b over the inorganic insulating layer 195a, and an inorganic insulating layer 195 c over the organic insulatinglayer 195 b.

An end portion of the inorganic insulating layer 195 a and an endportion of the inorganic insulating layer 195 c extend beyond an endportion of the organic insulating layer 195 b and are in contact witheach other. The inorganic insulating layer 195 a is in contact with theinsulating layer 215 (inorganic insulating layer) through the opening inthe insulating layer 214 (organic insulating layer). Accordingly, thelight-receiving element 110 and the light-emitting element 190 can besurrounded by the insulating layer 215 and the protective layer 195, sothat the reliability of the light-receiving element 110 and thelight-emitting element 190 can be increased.

As described above, the protective layer 195 may have a stacked-layerstructure of an organic insulating film and an inorganic insulatingfilm. In that case, an end portion of the inorganic insulating filmpreferably extends beyond an end portion of the organic insulating film.

The lens 149 is provided on the surface of the substrate 152 on thesubstrate 151 side. The lens 149 has the convex surface on the substrate151 side. It is preferable that the light-receiving region of thelight-receiving element 110 overlap with the lens 149 and do not overlapwith the light-emitting layer 193. Thus, the sensitivity and accuracy ofthe sensor using the light-receiving element 110 can be increased.

The lens 149 preferably has a refractive index of higher than or equalto 1.3 and lower than or equal to 2.5 with respect to the wavelength oflight received by the light-receiving element 110. The lens 149 can beformed using at least one of an inorganic material and an organicmaterial. For example, a material containing a resin can be used for thelens 149. Moreover, a material containing at least one of an oxide and asulfide can be used for the lens 149.

Specifically, a resin containing chlorine, bromine, or iodine, a resincontaining a heavy metal atom, a resin having an aromatic ring, a resincontaining sulfur, or the like can be used for the lens 149.Alternatively, a material containing a resin and nanoparticles of amaterial having a higher refractive index than the resin can be used forthe lens 149. Titanium oxide, zirconium oxide, or the like can be usedfor the nanoparticles.

Alternatively, cerium oxide, hafnium oxide, lanthanum oxide, magnesiumoxide, niobium oxide, tantalum oxide, titanium oxide, yttrium oxide,zinc oxide, an oxide containing indium and tin, an oxide containingindium, gallium, and zinc, or the like can be used for the lens 149.Alternatively, zinc sulfide or the like can be used for the lens 149.

In the display panel 200B, the protective layer 195 and the substrate152 are attached to each other with the adhesive layer 142. The adhesivelayer 142 is provided to overlap with the light-receiving element 110and the light-emitting element 190, and the display panel 200B has asolid sealing structure.

Structure Example 3-3

FIG. 22A is a cross-sectional view of a display panel 200C. The displaypanel 200C differs from the display panel 200B mainly in the transistorstructure and including neither the light-blocking layer BM nor the lens149.

The display panel 200C includes a transistor 208, a transistor 209, anda transistor 210 over the substrate 151.

The transistors 208, 209, and 210 each include the conductive layer 221functioning as a gate, the insulating layer 211 functioning as a gateinsulating layer, a semiconductor layer including a channel formationregion 231 i and a pair of low-resistance regions 231 n, the conductivelayer 222 a connected to one of the pair of low-resistance regions 231n, the conductive layer 222 b connected to the other of the pair oflow-resistance regions 231 n, an insulating layer 225 functioning as agate insulating layer, the conductive layer 223 functioning as a gate,and the insulating layer 215 covering the conductive layer 223. Theinsulating layer 211 is positioned between the conductive layer 221 andthe channel formation region 231 i. The insulating layer 225 ispositioned between the conductive layer 223 and the channel formationregion 231 i.

The conductive layer 222 a and the conductive layer 222 b are connectedto the low-resistance regions 231 n through openings provided in theinsulating layer 225 and the insulating layer 215. One of the conductivelayer 222 a and the conductive layer 222 b functions as a source, andthe other of the conductive layer 222 a and the conductive layer 222 bfunctions as a drain.

The pixel electrode 191 of the light-emitting element 190 iselectrically connected to one of the pair of low-resistance regions 231n of the transistor 208 through the conductive layer 222 b.

The pixel electrode 111 of the light-receiving element 110 iselectrically connected to the other of the pair of low-resistanceregions 231 n of the transistor 209 through the conductive layer 222 b.

FIG. 22A shows an example in which the insulating layer 225 covers a topsurface and a side surface of the semiconductor layer. FIG. 22B shows anexample in which the insulating layer 225 overlaps with the channelformation region 231 i of the semiconductor layer 231 and does notoverlap with the low-resistance regions 231 n. The structure shown inFIG. 22B can be obtained by processing the insulating layer 225 usingthe conductive layer 223 as a mask, for example. In FIG. 22B, theinsulating layer 215 is provided to cover the insulating layer 225 andthe conductive layer 223, and the conductive layer 222 a and theconductive layer 222 b are connected to the low-resistance regions 231 nthrough openings in the insulating layer 215. Furthermore, an insulatinglayer 218 covering the transistor may be provided.

Structure Example 3-4

FIG. 23 is a cross-sectional view of a display panel 200D. The displaypanel 200D differs from the display panel 200C mainly in the substratestructure.

The display panel 200D includes neither the substrate 151 nor thesubstrate 152 and includes the substrate 153, the substrate 154, theadhesive layer 155, and the insulating layer 212.

The substrate 153 and the insulating layer 212 are attached to eachother with the adhesive layer 155. The substrate 154 and the protectivelayer 195 are attached to each other with the adhesive layer 142.

The display panel 200D is formed in such a manner that the insulatinglayer 212, the transistor 208, the transistor 209, the light-receivingelement 110, the light-emitting element 190, and the like that areformed over a formation substrate are transferred onto the substrate153. The substrate 153 and the substrate 154 are preferably flexible.Accordingly, the display panel 200D can be highly flexible.

The inorganic insulating film that can be used for the insulating layer211, the insulating layer 213, and the insulating layer 215 can be usedfor the insulating layer 212. Alternatively, a stacked film of anorganic insulating film and an inorganic insulating film may be used forthe insulating layer 212. In that case, a film on the transistor 209side is preferably an inorganic insulating film.

The above is the description of the structure examples of the displaypanel.

[Metal Oxide]

A metal oxide that can be used for the semiconductor layer is describedbelow.

Note that in this specification and the like, a metal oxide containingnitrogen is also referred to as a metal oxide in some cases. Inaddition, a metal oxide containing nitrogen may be referred to as ametal oxynitride. For example, a metal oxide containing nitrogen, suchas zinc oxynitride (ZnON), may be used for the semiconductor layer.

Note that the terms “CAAC (c-axis aligned crystal)” and “CAC(cloud-aligned composite)” might appear in this specification and thelike. CAAC refers to an example of a crystal structure, and CAC refersto an example of a function or a material composition.

For example, a cloud-aligned composite oxide semiconductor (CAC-OS) canbe used for the semiconductor layer.

A CAC-OS or a CAC-metal oxide has a conducting function in part of thematerial and has an insulating function in another part of the material;as a whole, the CAC-OS or the CAC-metal oxide has a function of asemiconductor. Note that in the case where the CAC-OS or the CAC-metaloxide is used in a semiconductor layer of a transistor, the conductingfunction is a function that allows electrons (or holes) serving ascarriers to flow, and the insulating function is a function that doesnot allow electrons serving as carriers to flow. By the complementaryaction of the conducting function and the insulating function, aswitching function (On/Off function) can be given to the CAC-OS or theCAC-metal oxide. In the CAC-OS or the CAC-metal oxide, separation of thefunctions can maximize each function.

Furthermore, the CAC-OS or the CAC-metal oxide includes conductiveregions and insulating regions. The conductive regions have the aboveconducting function, and the insulating regions have the aboveinsulating function. Furthermore, in some cases, the conductive regionsand the insulating regions in the material are separated at thenanoparticle level. Furthermore, in some cases, the conductive regionsand the insulating regions are unevenly distributed in the material.Furthermore, the conductive regions are observed to be coupled in acloud-like manner with their boundaries blurred, in some cases.

Furthermore, in the CAC-OS or the CAC-metal oxide, the conductiveregions and the insulating regions each have a size greater than orequal to 0.5 nm and less than or equal to 10 nm, preferably greater thanor equal to 0.5 nm and less than or equal to 3 nm, and are dispersed inthe material, in some cases.

Furthermore, the CAC-OS or the CAC-metal oxide includes componentshaving different bandgaps. For example, the CAC-OS or the CAC-metaloxide includes a component having a wide gap due to the insulatingregion and a component having a narrow gap due to the conductive region.In the case of the structure, when carriers flow, carriers mainly flowthrough the component having a narrow gap. Furthermore, the componenthaving a narrow gap complements the component having a wide gap, andcarriers also flow through the component having a wide gap inconjunction with the component having a narrow gap. Therefore, in thecase where the CAC-OS or the CAC-metal oxide is used for the channelformation region of the transistor, high current drive capability in anon state of the transistor, that is, high on-state current and highfield-effect mobility can be obtained.

In other words, the CAC-OS or the CAC-metal oxide can also be referredto as a matrix composite or a metal matrix composite.

Oxide semiconductors (metal oxides) are classified into a single crystaloxide semiconductor and a non-single crystal oxide semiconductor.Examples of a non-single crystal oxide semiconductor include a CAAC-OS(c-axis aligned crystalline oxide semiconductor), a polycrystallineoxide semiconductor, an nc-OS (nanocrystalline oxide semiconductor), anamorphous-like oxide semiconductor (a-like OS), and an amorphous oxidesemiconductor.

The CAAC-OS has c-axis alignment, a plurality of nanocrystals areconnected in the a-b plane direction, and its crystal structure hasdistortion. Note that the distortion refers to a portion where thedirection of lattice arrangement changes between a region with regularlattice arrangement and another region with regular lattice arrangementin a region where the plurality of nanocrystals are connected.

The nanocrystal is basically a hexagon but is not always a regularhexagon and is a non-regular hexagon in some cases. Furthermore,pentagonal lattice arrangement, heptagonal lattice arrangement, and thelike are included in the distortion in some cases. Note that it isdifficult to observe a clear crystal grain boundary (also referred to asgrain boundary) even in the vicinity of distortion in the CAAC-OS. Thatis, formation of a crystal grain boundary is inhibited by the distortionof lattice arrangement. This is because the CAAC-OS can toleratedistortion owing to the low density of oxygen atom arrangement in thea-b plane direction, a change in interatomic bond distance byreplacement of a metal element, and the like.

Furthermore, the CAAC-OS tends to have a layered crystal structure (alsoreferred to as a layered structure) in which a layer containing indiumand oxygen (hereinafter referred to as an In layer) and a layercontaining the element M, zinc, and oxygen (hereinafter referred to asan (M,Zn) layer) are stacked. Note that indium and the element M can bereplaced with each other, and when the element M in the (M,Zn) layer isreplaced with indium, the layer can also be referred to as an (In,M,Zn)layer. Furthermore, when indium in the In layer is replaced with theelement M, the layer can be referred to as an (In,M) layer.

The CAAC-OS is a metal oxide with high crystallinity. Meanwhile, in theCAAC-OS, it can be said that a reduction in electron mobility due to thecrystal grain boundary is less likely to occur because it is difficultto observe a clear crystal grain boundary. Furthermore, the mixing ofimpurities, formation of defects, or the like might decrease thecrystallinity of the metal oxide; thus, it can also be said that theCAAC-OS is a metal oxide having small amounts of impurities and defects(e.g., oxygen vacancies (Vo)). Thus, a metal oxide including a CAAC-OSis physically stable. Therefore, the metal oxide including a CAAC-OS isresistant to heat and has high reliability.

In the nc-OS, a microscopic region (for example, a region with a sizegreater than or equal to 1 nm and less than or equal to 10 nm, inparticular, a region with a size greater than or equal to 1 nm and lessthan or equal to 3 nm) has periodic atomic arrangement. Furthermore,there is no regularity of crystal orientation between differentnanocrystals in the nc-OS. Thus, the orientation in the whole film isnot observed. Accordingly, the nc-OS cannot be distinguished from ana-like OS or an amorphous oxide semiconductor depending on the analysismethod.

Note that indium-gallium-zinc oxide (hereinafter referred to as IGZO)that is a kind of metal oxide containing indium, gallium, and zinc has astable structure in some cases when formed of the nanocrystals. Inparticular, IGZO crystals tend not to grow in the air and thus, a stablestructure is obtained in some cases when IGZO is formed of smallercrystals (e.g., the nanocrystals) rather than larger crystals (here,crystals with a size of several millimeters or several centimeters).

The a-like OS is a metal oxide that has a structure between those of thenc-OS and the amorphous oxide semiconductor. The a-like OS includes avoid or a low-density region. That is, the a-like OS has lowercrystallinity than the nc-OS and the CAAC-OS.

An oxide semiconductor (a metal oxide) has various structures withdifferent properties. Two or more kinds of the amorphous oxidesemiconductor, the polycrystalline oxide semiconductor, the a-like OS,the nc-OS, and the CAAC-OS may be included in an oxide semiconductor ofone embodiment of the present invention.

A metal oxide film that functions as a semiconductor layer can bedeposited using either or both of an inert gas and an oxygen gas. Notethat there is no particular limitation on the flow rate ratio of oxygen(the partial pressure of oxygen) at the time of deposition of the metaloxide film. However, to obtain a transistor having high field-effectmobility, the flow rate ratio of oxygen (the partial pressure of oxygen)at the time of deposition of the metal oxide film is preferably higherthan or equal to 0% and lower than or equal to 30%, further preferablyhigher than or equal to 5% and lower than or equal to 30%, still furtherpreferably higher than or equal to 7% and lower than or equal to 15%.

The energy gap of the metal oxide is preferably greater than or equal to2 eV, further preferably greater than or equal to 2.5 eV, still furtherpreferably greater than or equal to 3 eV. With the use of a metal oxidehaving such a wide energy gap, the off-state current of the transistorcan be reduced.

The substrate temperature during the deposition of the metal oxide filmis preferably lower than or equal to 350° C., further preferably higherthan or equal to room temperature and lower than or equal to 200° C.,still further preferably higher than or equal to room temperature andlower than or equal to 130° C. The substrate temperature during thedeposition of the metal oxide film is preferably room temperaturebecause productivity can be increased.

The metal oxide film can be formed by a sputtering method.Alternatively, a PLD method, a PECVD method, a thermal CVD method, anALD method, a vacuum evaporation method, or the like may be used.

The above is the description of the metal oxide.

At least part of this embodiment can be implemented in combination withany of the other embodiments described in this specification asappropriate.

Embodiment 3

In this embodiment, electronic devices that are examples of oneembodiment of the present invention will be described with reference toFIGS. 24A to 26F.

Electronic devices of this embodiment each include the display deviceaccording to one embodiment of the present invention. The display devicehas a function of detecting light, and thus can perform biologicalauthentication with a display portion or detect touch or near touch onthe display portion. An electronic device according to one embodiment ofthe present invention is an electronic device that is difficult to abuseand has extremely high security. In addition, the electronic device canincrease its functionality and convenience, for example.

Examples of electronic devices include a digital camera, a digital videocamera, a digital photo frame, a cellular phone, a portable gamemachine, a portable information terminal, and an audio reproducingdevice in addition to electronic devices provided with comparativelylarge screens, such as a television device, a desktop or laptop personalcomputer, a monitor for a computer or the like, digital signage, and alarge game machine like a pachinko machine.

The electronic devices of this embodiment may each include a sensor (asensor having a function of measuring force, displacement, position,speed, acceleration, angular velocity, rotational frequency, distance,light, liquid, magnetism, temperature, a chemical substance, sound,time, hardness, an electric field, current, voltage, power, radioactiverays, flow rate, humidity, a gradient, oscillation, odor, or infraredrays).

The electronic devices of this embodiment can each have a variety offunctions. For example, the electronic devices of this embodiment caneach have a function of displaying a variety of information (a stillimage, a moving image, a text image, and the like) on the displayportion, a touch panel function, a function of displaying a calendar,date, time, and the like, a function of executing a variety of software(programs), a wireless communication function, a function of reading aprogram or data stored in a recording medium, and the like.

An electronic device 6500 shown in FIG. 24A is a portable informationterminal that can be used as a smartphone.

The electronic device 6500 includes a housing 6501, a display portion6502, a power button 6503, buttons 6504, a speaker 6505, a microphone6506, a camera 6507, a light source 6508, and the like. The displayportion 6502 has a touch panel function.

The display device according to one embodiment of the present inventioncan be used in the display portion 6502.

FIG. 24B is a schematic cross-sectional view including an end portion ofthe housing 6501 on the microphone 6506 side.

A protective component 6510 having a light-transmitting property isprovided on the display surface side of the housing 6501. A displaypanel 6511, an optical component 6512, a touch sensor panel 6513, aprinted circuit board 6517, a battery 6518, and the like are provided ina space surrounded by the housing 6501 and the protective component6510.

The display panel 6511, the optical component 6512, and the touch sensorpanel 6513 are fixed to the protective component 6510 with an adhesivelayer (not illustrated).

Part of the display panel 6511 is folded back in a region outside thedisplay portion 6502, and an FPC 6515 is connected to the part that isfolded back. An IC 6516 is mounted on the FPC 6515. The FPC 6515 isconnected to a terminal provided on the printed circuit board 6517.

A flexible display according to one embodiment of the present inventioncan be used for the display panel 6511. Thus, an extremely lightweightelectronic device can be provided. The display panel 6511 is extremelythin, so that the battery 6518 with high capacity can be mounted whilemaintaining the small thickness of the electronic device. An electronicdevice with a narrow frame can be obtained when part of the displaypanel 6511 is folded back so that the portion connected to the FPC 6515is positioned on the rear side of a pixel portion.

FIG. 25A shows an example of a television device. In a television device7100, a display portion 7000 is incorporated in a housing 7101. Here, astructure in which the housing 7101 is supported by a stand 7103 isshown.

The display device according to one embodiment of the present inventioncan be used in the display portion 7000.

Operation of the television device 7100 shown in FIG. 25A can beperformed with an operation switch provided in the housing 7101 or aseparate remote control 7111. Alternatively, the display portion 7000may include a touch sensor, and the television device 7100 may beoperated by touch on the display portion 7000 with a finger or the like.The remote control 7111 may be provided with a display portion fordisplaying information output from the remote control 7111. Withoperation keys or a touch panel provided in the remote control 7111,channels and volume can be operated and videos displayed on the displayportion 7000 can be operated.

Note that the television device 7100 has a structure in which areceiver, a modem, and the like are provided. A general televisionbroadcast can be received with the receiver. In addition, when connectedto a communication network with or without wires via the modem, one-way(from a transmitter to a receiver) or two-way (between a transmitter anda receiver or between receivers) information communication can also beperformed.

FIG. 25B shows an example of a laptop personal computer. A laptoppersonal computer 7200 includes a housing 7211, a keyboard 7212, apointing device 7213, an external connection port 7214, and the like. Inthe housing 7211, the display portion 7000 is incorporated.

The display device according to one embodiment of the present inventioncan be used in the display portion 7000.

FIGS. 25C and 25D show examples of digital signage.

Digital signage 7300 shown in FIG. 25C includes a housing 7301, thedisplay portion 7000, a speaker 7303, and the like. Furthermore, thedigital signage 7300 can include an LED lamp, an operation key(including a power switch or an operation switch), a connectionterminal, a variety of sensors, a microphone, and the like.

FIG. 25D is digital signage 7400 attached to a cylindrical pillar 7401.The digital signage 7400 includes the display portion 7000 providedalong a curved surface of the pillar 7401.

The display device according to one embodiment of the present inventioncan be used in the display portion 7000 in FIGS. 25C and 25D.

The larger display portion 7000 can increase the amount of informationthat can be provided at a time. In addition, the larger display portion7000 attracts more attention, so that the effect of advertising can beincreased, for example.

It is preferable to use a touch panel in the display portion 7000because in addition to display of a still image or a moving image on thedisplay portion 7000, intuitive operation by a user is possible.Moreover, for an application for providing information such as routeinformation or traffic information, usability can be enhanced byintuitive operation.

Furthermore, as shown in FIGS. 25C and 25D, it is preferable that thedigital signage 7300 or the digital signage 7400 work with aninformation terminal 7311 or an information terminal 7411 such as asmartphone a user has through wireless communication. For example,information of an advertisement displayed on the display portion 7000can be displayed on a screen of the information terminal 7311 or theinformation terminal 7411. Moreover, by operation of the informationterminal 7311 or the information terminal 7411, a displayed image on thedisplay portion 7000 can be switched.

Furthermore, it is possible to make the digital signage 7300 or thedigital signage 7400 execute a game with the use of the screen of theinformation terminal 7311 or the information terminal 7411 as anoperation means (controller). Thus, an unspecified number of users canjoin in and enjoy the game concurrently.

Electronic devices shown in FIGS. 26A to 26F include a housing 9000, adisplay portion 9001, a speaker 9003, an operation key 9005 (including apower switch or an operation switch), a connection terminal 9006, asensor 9007 (a sensor having a function of measuring force,displacement, a position, speed, acceleration, angular velocity,rotational frequency, distance, light, liquid, magnetism, temperature, achemical substance, sound, time, hardness, an electric field, current,voltage, power, radiation, flow rate, humidity, a gradient, oscillation,an odor, or infrared rays), a microphone 9008, and the like.

The electronic devices shown in FIGS. 26A to 26F have a variety offunctions. For example, the electronic devices can have a function ofdisplaying a variety of data (a still image, a moving image, a textimage, and the like) on the display portion, a touch panel function, afunction of displaying a calendar, date, time, and the like, a functionof controlling processing with a variety of software (programs), awireless communication function, a function of reading out andprocessing a program or data stored in a recording medium, and the like.Note that the functions of the electronic devices are not limitedthereto, and the electronic devices can have a variety of functions. Theelectronic devices may include a plurality of display portions. Inaddition, the electronic devices may each include a camera or the likeand have a function of taking a still image or a moving image andstoring the taken image in a recording medium (an external recordingmedium or a recording medium incorporated in the camera), a function ofdisplaying the taken image on the display portion, or the like.

The details of the electronic devices shown in FIGS. 26A to 26F aredescribed below.

FIG. 26A is a perspective view showing a portable information terminal9101. For example, the portable information terminal 9101 can be used asa smartphone. Note that the portable information terminal 9101 may beprovided with the speaker 9003, the connection terminal 9006, the sensor9007, or the like. In addition, the portable information terminal 9101can display characters and image information on its plurality ofsurfaces. FIG. 26A shows an example in which three icons 9050 aredisplayed. Furthermore, information 9051 indicated by dashed rectanglescan be displayed on another surface of the display portion 9001.Examples of the information 9051 include notification of reception of ane-mail, SNS, or an incoming call, the title and sender of an e-mail,SNS, or the like, the date, the time, remaining battery, and thereception strength of an antenna. Alternatively, the icon 9050 or thelike may be displayed in a position where the information 9051 isdisplayed.

FIG. 26B is a perspective view showing a portable information terminal9102. The portable information terminal 9102 has a function ofdisplaying information on three or more surfaces of the display portion9001. Here, an example in which information 9052, information 9053, andinformation 9054 are displayed on different surfaces is shown. Forexample, the user can also check the information 9053 displayed in aposition that can be observed from above the portable informationterminal 9102, with the portable information terminal 9102 put in abreast pocket of his/her clothes. The user can see the display withouttaking out the portable information terminal 9102 from the pocket anddecide whether to answer a call, for example.

FIG. 26C is a perspective view showing a watch-type portable informationterminal 9200. In addition, a display surface of the display portion9001 is curved and provided, and display can be performed along thecurved display surface. Furthermore, intercommunication between theportable information terminal 9200 and, for example, a headset capableof wireless communication enables hands-free calling. Moreover, with theconnection terminal 9006, the portable information terminal 9200 canalso perform mutual data transmission with another information terminaland charging. Note that charging operation may be performed by wirelesspower feeding.

FIGS. 26D, 26E, and 26F are perspective views showing a foldableportable information terminal 9201. In addition, FIG. 26D is aperspective view of an unfolded state of the portable informationterminal 9201, FIG. 26F is a perspective view of a folded state thereof,and FIG. 26E is a perspective view of a state in the middle of changefrom one of FIGS. 26D and 26F to the other. The portable informationterminal 9201 is highly portable in the folded state and is highlybrowsable in the unfolded state because of a seamless large displayregion. The display portion 9001 of the portable information terminal9201 is supported by three housings 9000 joined with hinges 9055. Forexample, the display portion 9001 can be bent with a radius of curvatureof greater than or equal to 0.1 mm and less than or equal to 150 mm.

At least part of this embodiment can be implemented in combination withany of the other embodiments described in this specification asappropriate.

Example

In this example, a display device according to one embodiment of thepresent invention was manufactured and results of imaging using thedisplay device were shown.

[Display Device]

The display device was manufactured by forming a transistor over a glasssubstrate and forming light-emitting elements and a light-receivingelement over the transistor. Furthermore, as a protective layer forprotecting the light-emitting elements and the light-receiving element,a film containing an organic resin was attached onto the light-emittingelements and the light-receiving element with an adhesive layertherebetween.

As the transistor, a top-gate transistor including an In-Ga—Zn-basedoxide for a semiconductor layer where a channel is formed was used. Thetransistor was manufactured over the glass substrate at a processtemperature lower than 500° C.

As the light-emitting elements, organic EL elements of red (R), green(G), and blue (B) were used. The light-emitting elements weretop-emission light-emitting elements. An organic photodiode was used asthe light-receiving element. A buffer layer and a common electrode wereshared by the organic EL elements and the organic photodiode. Each ofthe light-emitting layers and an active layer were formed separately bya vacuum evaporation method using a metal mask.

As circuits for driving the light-emitting elements, the circuits shownin FIG. 4B and FIG. 7 were used. As a circuit for driving thelight-receiving element, the circuit shown in FIG. 12 was used.

The display device includes a display portion with a screen diagonal of7.99 inches, a pixel count of 1080×2160, a pixel size of 84 μm×84 μm,and a resolution of 302 ppi. The display device includes a gate driverfor image display, a demultiplexer, a scan driver for a sensor, a readcircuit, and the like, and further includes a source driver for imagedisplay, an AD converter circuit, and the like as external circuits.

[Imaging]

Imaging was performed while a palm was put on a display surface of thedisplay device. Imaging was performed using the green light-emittingelement as a light source while the green light-emitting element wasemitting light. After that, obtained image data was subjected tosmoothing processing for noise removal and contrast adjustment forimprovement in visibility.

FIG. 27A shows a captured image. FIG. 27B is an enlarged image of aregion P shown in FIG. 27A, and FIG. 27C is an enlarged image of aregion Q shown in FIG. 27A.

Note that in FIGS. 27A, 27B, and 27C, mosaic processing was performed onparts of the images to protect personal information.

According to one embodiment of the present invention, the size of animaging region can be increased and the entire display region can serveas the imaging region; therefore, as shown in FIG. 27A, a clear image ofthe palm and a tip of each finger can be captured by one-time imaging.

According to one embodiment of the present invention, pixel density canbe increased throughout the imaging region (the display region). Thus,even in the region Q that is near the center of the imaging region andin the region P that is near an end portion of the imaging region, clearimages of a fingerprint and a palm print can be captured, as shown inFIGS. 27C and 27B.

As described above, it was confirmed that the display device accordingto one embodiment of the present invention not only can display imagesbut also can capture clear images of objects that are in contact withthe display surface. Thus, the display device is suitably used forbiological authentication such as fingerprint authentication or palmprint authentication. In addition, the display device can also be usedas an extremely thin image scanner that does not require a separatelight source.

This application is based on Japanese Patent Application Serial No.2019-157094 filed with Japan Patent Office on Aug. 29, 2019 and JapanesePatent Application Serial No. 2020-082434 filed with Japan Patent Officeon May 8, 2020, the entire contents of which are hereby incorporated byreference.

What is claimed is:
 1. A display device comprising: a first pixelcomprising a first transistor, a second transistor, a third transistor,a fourth transistor, a first capacitor, a second capacitor, and a firstlight-emitting element; and a second pixel comprising a fifthtransistor, a sixth transistor, and a second light-emitting element,wherein one of a source and a drain of the first transistor iselectrically connected to a gate of the second transistor and oneelectrode of the first capacitor, wherein one of a source and a drain ofthe second transistor is electrically connected to the firstlight-emitting element, wherein one of a source and a drain of the thirdtransistor and one of a source and a drain of the fourth transistor areelectrically connected to a first wiring, wherein the other of thesource and the drain of the third transistor is electrically connectedto the other electrode of the first capacitor, wherein the other of thesource and the drain of the fourth transistor is electrically connectedto the first light-emitting element, wherein one electrode of the secondcapacitor is electrically connected to the gate of the secondtransistor, wherein the other electrode of the second capacitor iselectrically connected to the one of the source and the drain of thesecond transistor, wherein one of a source and a drain of the fifthtransistor and one of a source and a drain of the sixth transistor areelectrically connected to the first wiring, and wherein the other of thesource and the drain of the sixth transistor is electrically connectedto the second light-emitting element.
 2. The display device according toclaim 1, wherein each of the first transistor, the second transistor,the third transistor, and the fourth transistor comprises an oxidesemiconductor in a channel formation region.
 3. The display deviceaccording to claim 1, further comprising a third pixel, wherein thethird pixel comprises a light-receiving element.
 4. The display deviceaccording to claim 1, wherein the other of the source and the drain ofthe first transistor is electrically connected to a second wiring,wherein a gate of the first transistor and a gate of the fourthtransistor are electrically connected to a third wiring, and wherein agate of the third transistor is electrically connected to a fourthwiring.
 5. The display device according to claim 1, wherein each of thefirst transistor, the second transistor, the third transistor, and thefourth transistor comprises a back gate.
 6. The display device accordingto claim 1, wherein the first pixel and the second pixel are positionedin different columns.
 7. A display device comprising: a first pixelcomprising a first transistor, a second transistor, a third transistor,a fourth transistor, a first capacitor, a second capacitor, and a firstlight-emitting element; and a second pixel comprising a fifthtransistor, a sixth transistor, and a second light-emitting element,wherein one of a source and a drain of the first transistor iselectrically connected to a gate of the second transistor and oneelectrode of the first capacitor, wherein one of a source and a drain ofthe second transistor is electrically connected to the firstlight-emitting element, wherein one of a source and a drain of the thirdtransistor is electrically connected to a first wiring, wherein theother of the source and the drain of the third transistor iselectrically connected to the other electrode of the first capacitor andone of a source and a drain of the fourth transistor, wherein the otherof the source and the drain of the fourth transistor is electricallyconnected to the first light-emitting element, wherein one electrode ofthe second capacitor is electrically connected to the gate of the secondtransistor, wherein the other electrode of the second capacitor iselectrically connected to the one of the source and the drain of thesecond transistor, wherein one of a source and a drain of the fifthtransistor is electrically connected to the first wiring, wherein theother of the source and the drain of the fifth transistor iselectrically connected to one of a source and a drain of the sixthtransistor, and wherein the other of the source and the drain of thesixth transistor is electrically connected to the second light-emittingelement.
 8. The display device according to claim 7, wherein each of thefirst transistor, the second transistor, the third transistor, and thefourth transistor comprises an oxide semiconductor in a channelformation region.
 9. The display device according to claim 7, furthercomprising a third pixel, wherein the third pixel comprises alight-receiving element.
 10. The display device according to claim 7,wherein the other of the source and the drain of the first transistor iselectrically connected to a second wiring, wherein a gate of the firsttransistor and a gate of the fourth transistor are electricallyconnected to a third wiring, and wherein a gate of the third transistoris electrically connected to a fourth wiring.
 11. The display deviceaccording to claim 7, wherein each of the first transistor, the secondtransistor, the third transistor, and the fourth transistor comprises aback gate.
 12. The display device according to claim 7, wherein thefirst pixel and the second pixel are positioned in different columns.